The ClearTempStorage() method of the transfer Adapter interface,
while implemented for most adapters, is never actually called,
and moreover is dangerous in some its current implementations
if it were ever to be called.

Specifically in the basic upload and download adapters and the
SSH adapter, the ClearTempStorage() method relies on an internal
tempDir() method to return the path to the temporary directory
to be cleared, which ClearTempStorage() then removes entirely.

The tempDir() methods, however, can return os.TempDir() if they
are unable to create a local temporary directory within the
Git LFS storage directory, and also do not cache the path to
the directory they first returned.  So were ClearTempStorage()
ever to be called in one of these adapters, its invocation of
tempDir() might just return the system temporary directory
(e.g., /tmp on Unix), which it would then attempt to remove.

The ClearTempStorage() method was introduced in commits
f124f05 and
940a91a of PR git-lfs#1265, but
has never been called by any user of the transfer
adapter interface.

We therefore just remove this method and its implemetations
from all the current tranfer adapters.

The ClearTempStorage() method of the transfer Adapter interface,
while implemented for most adapters, is never actually called,
and moreover is dangerous in some its current implementations
if it were ever to be called.

Specifically in the basic upload and download adapters and the
SSH adapter, the ClearTempStorage() method relies on an internal
tempDir() method to return the path to the temporary directory
to be cleared, which ClearTempStorage() then removes entirely.

The tempDir() methods, however, can return os.TempDir() if they
are unable to create a local temporary directory within the
Git LFS storage directory, and also do not cache the path to
the directory they first returned.  So were ClearTempStorage()
ever to be called in one of these adapters, its invocation of
tempDir() might just return the system temporary directory
(e.g., /tmp on Unix), which it would then attempt to remove.

The ClearTempStorage() method was introduced in commits
f124f05 and
940a91a of PR git-lfs#1265, but
has never been called by any user of the transfer
adapter interface.

We therefore just remove this method and its implemetations
from all the current tranfer adapters.

The three test functions in the tq/transfer_test.go source file are
all named with the prefix "test" rather than "Test", and as a result,
do not actually execute.  This oversight dates from the original
introduction of these tests in the "transfer" package in commit
10623f5 of PR git-lfs#1265.  (The package
was later renamed to the current "tq" package in commit
891db97 of PR git-lfs#1780.)

We therefore change the test function names to begin with "Test",
and resolve several test regressions which have accumulated since the
tests were first added.

First, the TestBasicAdapterExists() function calls the
GetDownloadAdapterNames() and GetUploadAdapterNames() methods of the
Manifest structure, and these now return the names of three transfer
adapter implementations rather than just the original "basic" one,
so we allow for all three names to appear in any order.  (The
"lfs-standalone-file" adapter was added in commit
bb05cf5 of PR git-lfs#3748, and the "ssh"
adapter was added in commit 594f8e3
of PR git-lfs#4446.)

Second, the TestAdapterRegAndOverride() function expects the
NewDownloadAdapter() and NewUploadAdapter() methods of the Manifest
structure to return nil if the provided name argument does not match
that of any registered transfer adapter.  However, this has not been
the behaviour of those methods since commit
c5c2a75 of PR git-lfs#1279, shortly after
the tests were first introduced in PR git-lfs#1265.  In that commit, the
NewAdapterOrDefault() method was added, and the NewDownloadAdapter()
and NewUploadAdapter() revised to call it, so they return the
default "basic" adapter if the requested name does not match a
registered adapter.  We therefore revise and expand the test to
account for this behaviour, and also make sure to directly test the
simpler NewAdapter() method, which retains the originally intended
behaviour and returns nil if it does not find a matching adapter
for the provided name argument.

The three test functions in the tq/transfer_test.go source file are
all named with the prefix "test" rather than "Test", and as a result,
do not actually execute.  This oversight dates from the original
introduction of these tests in the "transfer" package in commit
10623f5 of PR git-lfs#1265.  (The package
was later renamed to the current "tq" package in commit
891db97 of PR git-lfs#1780.)

We therefore change the test function names to begin with "Test",
and resolve several test regressions which have accumulated since the
tests were first added.

First, the TestBasicAdapterExists() function calls the
GetDownloadAdapterNames() and GetUploadAdapterNames() methods of the
Manifest structure, and these now return the names of three transfer
adapter implementations rather than just the original "basic" one,
so we allow for all three names to appear in any order.  (The
"lfs-standalone-file" adapter was added in commit
bb05cf5 of PR git-lfs#3748, and the "ssh"
adapter was added in commit 594f8e3
of PR git-lfs#4446.)

Second, the TestAdapterRegAndOverride() function expects the
NewDownloadAdapter() and NewUploadAdapter() methods of the Manifest
structure to return nil if the provided name argument does not match
that of any registered transfer adapter.  However, this has not been
the behaviour of those methods since commit
c5c2a75 of PR git-lfs#1279, shortly after
the tests were first introduced in PR git-lfs#1265.  In that commit, the
NewAdapterOrDefault() method was added, and the NewDownloadAdapter()
and NewUploadAdapter() revised to call it, so they return the
default "basic" adapter if the requested name does not match a
registered adapter.  We therefore revise and expand the test to
account for this behaviour, and also make sure to directly test the
simpler NewAdapter() method, which retains the originally intended
behaviour and returns nil if it does not find a matching adapter
for the provided name argument.

Third, the TestAdapterRegButBasicOnly() function, which passes without
changes, no longer fully performs the checks it was intended to make,
since the NewDownloadAdapter() and NewUploadAdapter() methods now always
return a non-nil value, so using a non-nil response from them to prove
that the "test" adapter is found is insufficient.  We therefore update
the test to confirm that the returned value from these functions is
a "test" adapter, as expected, and not just a "basic" one.

We also replace the use of the BasicAdapterName variable with the
"basic" string to align with the other tests.

The three test functions in the tq/transfer_test.go source file are
all named with the prefix "test" rather than "Test", and as a result,
do not actually execute.  This oversight dates from the original
introduction of these tests in the "transfer" package in commit
10623f5 of PR git-lfs#1265.  (The package
was later renamed to the current "tq" package in commit
891db97 of PR git-lfs#1780.)

We therefore change the test function names to begin with "Test",
and resolve several test regressions which have accumulated since the
tests were first added.

First, the TestBasicAdapterExists() function calls the
GetDownloadAdapterNames() and GetUploadAdapterNames() methods of the
Manifest structure, and these now return the names of three transfer
adapter implementations rather than just the original "basic" one,
so we allow for all three names to appear in any order.  (The
"lfs-standalone-file" adapter was added in commit
bb05cf5 of PR git-lfs#3748, and the "ssh"
adapter was added in commit 594f8e3
of PR git-lfs#4446.)

Second, the TestAdapterRegAndOverride() function expects the
NewDownloadAdapter() and NewUploadAdapter() methods of the Manifest
structure to return nil if the provided name argument does not match
that of any registered transfer adapter.  However, this has not been
the behaviour of those methods since commit
c5c2a75 of PR git-lfs#1279, shortly after
the tests were first introduced in PR git-lfs#1265.  In that commit, the
NewAdapterOrDefault() method was added, and the NewDownloadAdapter()
and NewUploadAdapter() methods revised to call it, so they return the
default "basic" adapter if the requested name does not match a
registered adapter.  We therefore revise and expand the test to
account for this behaviour, and also make sure to directly test the
underlying NewAdapter() method, which retains the originally intended
behaviour and returns nil if it does not find a matching adapter
for the provided name argument.

Third, although the TestAdapterRegButBasicOnly() function passes without
changes, it no longer fully performs the checks it was intended to make,
since the NewDownloadAdapter() and NewUploadAdapter() methods now always
return a non-nil value, so using a non-nil response from them to prove
that the "test" adapter was found is insufficient.  We therefore update
the test to confirm that the returned value from these functions is
a "test" adapter, as expected, and not just a "basic" one.

We also replace the use of the BasicAdapterName variable with the
"basic" string to align with the other tests.

We added initial support for the deduplication of Git LFS object files
between the Git working tree and our internal Git LFS storage directories
in commit ea16fd5 of PR git-lfs#952, using
the copy-on-write reflink functionality provided by the Linux Btrfs
filesystem.

Since we didn't implement equivalent capabilities for any other operating
systems, we defined two versions of a new CloneFile() function in our
"lfs" package, one for Linux, and one for all other types of systems.

Later, in commit 1ef2d43 of PR git-lfs#1265,
we moved the CopyWithCallback() function from our "lfs" package into our
"tools" package, so it would be more widely available for use in our
code base.  In that same PR, for instance, the function was first used
outside of the "lfs" package, in the download() method of what is now
the basicDownloadAdapter in our "tq" package.

Because the only caller of the CloneFile() function at the time was the
CopyWithCallback() function, both versions of the function were copied
to the "tools" package in commit 1ef2d43.

However, while the Linux version was completely moved to the "tools"
package by renaming the lfs/util_linux.go source file, the generic
version was only copied to a new tools/util_generic.go source file,
leaving the original lfs/util_generic.go in place.

As the lfs/util_generic.go source file and the CloneFile() function it
defines within the "lfs" package are no longer used, we can simply
delete them now.

The three test functions in the tq/transfer_test.go source file are
all named with the prefix "test" rather than "Test", and as a result,
do not actually execute.  This oversight dates from the original
introduction of these tests in the "transfer" package in commit
10623f5 of PR git-lfs#1265.  (The package
was later renamed to the current "tq" package in commit
891db97 of PR git-lfs#1780.)

We therefore change the test function names to begin with "Test",
and resolve several test regressions which have accumulated since the
tests were first added.

First, the TestBasicAdapterExists() function calls the
GetDownloadAdapterNames() and GetUploadAdapterNames() methods of the
Manifest structure, and these now return the names of three transfer
adapter implementations rather than just the original "basic" one,
so we allow for all three names to appear in any order.  (The
"lfs-standalone-file" adapter was added in commit
bb05cf5 of PR git-lfs#3748, and the "ssh"
adapter was added in commit 594f8e3
of PR git-lfs#4446.)

Second, the TestAdapterRegAndOverride() function expects the
NewDownloadAdapter() and NewUploadAdapter() methods of the Manifest
structure to return nil if the provided name argument does not match
that of any registered transfer adapter.  However, this has not been
the behaviour of those methods since commit
c5c2a75 of PR git-lfs#1279, shortly after
the tests were first introduced in PR git-lfs#1265.  In that commit, the
NewAdapterOrDefault() method was added, and the NewDownloadAdapter()
and NewUploadAdapter() methods revised to call it, so they return the
default "basic" adapter if the requested name does not match a
registered adapter.  We therefore revise and expand the test to
account for this behaviour, and also make sure to directly test the
underlying NewAdapter() method, which retains the originally intended
behaviour and returns nil if it does not find a matching adapter
for the provided name argument.

Third, although the TestAdapterRegButBasicOnly() function passes without
changes, it no longer fully performs the checks it was intended to make,
since the NewDownloadAdapter() and NewUploadAdapter() methods now always
return a non-nil value, so using a non-nil response from them to prove
that the "test" adapter was found is insufficient.  We therefore update
the test to confirm that the returned value from these functions is
a "test" adapter, as expected, and not just a "basic" one.

We also replace the use of the BasicAdapterName variable with the
"basic" string to align with the other tests.