FreeBSD CI is currently broken with this error

```
[4/4] Extracting curl-7.88.1: .......... done
curl https://sh.rustup.rs -sSf --output rustup.sh
ld-elf.so.1: /usr/local/lib/libcurl.so.4: Undefined symbol "nghttp2_option_set_no_rfc9113_leading_and_trailing_ws_validation"
```

From some quick searches I found [this bug] which looks related, but I
didn't see anything in the discussion which would let us work around the
problem.

[this bug]: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=269253

* Remove an unneeded doc, fixing the doc build on stable Rust.

Remove a doc comment which is redundant because it's on a re-export of
an item which already has its own doc comment. This also happens to work
around a bug in at least Rust 1.69.

Fixes #624.

* In the Rust 1.48 CI, pin tempfile to 3.4.0.

tempfile 3.5.0 depends on rustix 0.37. Pin to tempfile 3.4.0 since it
uses rustix 0.36 as this is the rustix 0.36 branch.

* Temporarily disable tests on Windows.

* Disable `test_backends` on Rust 1.48.

* Disable FreeBSD CI for now. (#530) (#600)

FreeBSD CI is currently broken with this error

```
[4/4] Extracting curl-7.88.1: .......... done
curl https://sh.rustup.rs -sSf --output rustup.sh
ld-elf.so.1: /usr/local/lib/libcurl.so.4: Undefined symbol "nghttp2_option_set_no_rfc9113_leading_and_trailing_ws_validation"
```

From some quick searches I found [this bug] which looks related, but I
didn't see anything in the discussion which would let us work around the
problem.

[this bug]: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=269253

…lliance#600)"

This reverts commit e8a49a2.

* Revert "Disable FreeBSD CI for now. (#530) (#600)"

This reverts commit e8a49a2.

* Fix FreeBSD CI failure