Auto merge of #29762 - mrobinson:remove-unused-python-code, r=jdm

Remove some unused python code

This change removes:
 - The custom `--dry-run` support for `cargo-update`. The real cargo command now has `--dry-run` support and this code was broken for Python 3.
- The Python 2 version of TemporaryDirectory. This is no longer needed as we require Python 3.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they do not change behavior.

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