In PR git-lfs#1839 we first developed our "lfsapi" package, and in commit
31f180b of that PR we introduced
the package's NewClient() function to initialize and return a Client
structure.

At the time, the NewClient() function invoked the ParseNetrc() function,
which was located in the same package.  As this function parsed a user's
"netrc" file, it could encounter error conditions, and so it might
return a non-nil "error" value.  The NewClient() function checked for
this possibility, and in the case of an error, would itself return a
non-nil "error" value.

However, in commit 1026ff0 of PR git-lfs#3307
we moved the ParseNetrc() function into our "creds" package, and added
the netrcCredentialHelper structure in that package.  In the same
commit we also refactored our handling of "netrc" files so that we
now parsed them when we retrieve credentials for an HTTP request,
rather than when we initialized a new Client structure in our "lfsapi"
package.

As a result, none of the remaining initialization steps in the
NewClient() function of the "lfsapi" package could encounter an error
condition, and so there was no specific need for the function to
continue to return an "error" value.

As this remains the case, we can simplify the NewClient() function
in our "lfsapi" package by just eliminating its "error" return value.

We then update all the callers of this function, including those in
our Go test functions, as they no longer need to check for an "error"
return value from the function.

In PR git-lfs#1769 we first developed our "locking" package, and in commit
4910706 of that PR we introduced
the package's NewClient() function to initialize and return a Client
structure.

At the conclusion of PR git-lfs#1769, the NewClient() function invoked both
the NewLockCache() function, which was also located in the "locking"
package, and the MkdirAll() function from the "os" package of the
Go standard library.  The NewClient() function called these functions
in order to create the "lockcache.db" file we store in the ".git/lfs"
directory.

Both the NewLockCache() and MkdirAll() functions could return
error conditions, and so might return non-nil "error" values.
The NewClient() function checked for these possibilities, and in
the case of an error, would itself return a non-nil "error" value.

However, in commit a998543 of PR git-lfs#1839
we revised the NewClient() function so that it did not create a
lock cache file.  Instead, this became the responsibility of a new
Client structure method named SetupFileCache().  We also added a
function to our "commands" package which first calls the "locking"
package's NewClient() function, and then invokes the SetupFileCache()
method on the newly initialized Client structure.

As a result, none of the remaining initialization steps in the
NewClient() function of the "locking" package could encounter an error
condition, and so there was no specific need for the function to
continue to return an "error" value.

As this remains the case, we can simplify the NewClient() function
in our "locking" package by just eliminating its "error" return value.

We then update all the callers of this function, including those in
our Go test functions, as they no longer need to check for an "error"
return value from the function.

As suggested by larsxschneider on PR review, we clarify the purpose
of the sshAuthClient structure in our "lfshttp" package by adding
a comment to describe its use, which is to execute the
"git-lfs-authenticate" command over SSH in order to fetch HTTP
credentials for the Git LFS Batch API.

Co-authored-by: Lars Schneider <larsxschneider@github.com>