Remove almost identical copies of methods already defined in distutils

[abravalheri]

Summary of changes

There are 2 methods defined for setuptools.Command that just look like copies of the ones defined in distutils.cmd.Command (except for formatting, rust auto-fixes). They seem to have been introduced in #1180.

https://www.diffchecker.com/w6na9oHI/

I am struggling to see the reason why we need to re-define them, unless the code was there just for backward compatibility with old Python versions (i.e. fixes were backported into distutils).

I can see however that this code exists since before Python 3.6...
It definetelly exists in the stdlib in 3.9 (minimum version supported by setuptools):

https://github.com/python/cpython/blob/3.9/Lib/distutils/cmd.py#L207-L215

https://github.com/python/cpython/blob/3.9/Lib/distutils/cmd.py#L223-L242

This PR tries to remove this code duplication.
If there is a reason for the duplication we should see regression tests failing.

Closes

Pull Request Checklist

• Changes have tests
• News fragment added in newsfragments/.
  (See documentation for details)

[abravalheri]

Possibly what happened is that in #1180 there was a subtle difference: it was using six.string_types instead of str.

However, with the move away from Python 2, the method returned to str and then became identical to the stdlib implementation.

[jaraco]

Yeah, there's a lot of code that can be consolidated once we can drop support for distutils from stdlib (which is approximately now, although I need to finish the deprecation/removal). Happy to see this incremental progress. Thanks!