Remove some deprecated code

[abravalheri]

Summary of changes

Remove code that has been deprecated for a while:

• Handling/warning about existing depends.txt (warning introduced in 2005)
• Auto-fixing broken egg_info directories, probably created by previous versions of setuptools (warning introduced in 2005)
• Deprecated backwards compatible APIs for easy_install (easy_install itself has been deprecated for a while).
• egg_info.get_pkg_info_revision, deprecated since 2015
• Ignoring invalid pyproject.toml: when pyproject.toml was introduced there were some people writing invalid files, ref (Projects that contain pyproject.toml not compliant with standards are failing on v61. #3199 and [Docs] Example may accidentally be encouraging users to write invalid pyproject.toml files cibuildwheel#1064). As a grace period was introduced for users to fix this up.
• dist._get_unpatched, deprecated since 2016.
• SVN support in setuptools.package_index (warning introduced in 2018).

Closes

Pull Request Checklist

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

[abravalheri]

Refs:

• Remove some deprecated code #3948 (comment)
• There seems to be a problem with the docs job in GHA jaraco/skeleton#82

[jaraco]

This code is maintained upstream in jaraco/skeleton. I'm not sure what it even means to have matrix.python and matrix.dev in this section. Probably these lines simply need to be removed upstream. But that still doesn't address the concern that building against the default Python causes problems for Setuptools. Probably this change deserves a comment linking to a bug as to why it's here, because by pinning a version, it creates cruft that someone will have to revisit in the future (maybe just link to the comment).

[abravalheri]

Thanks Jason.

I changed the PR to avoid modifying the workflow.

I believe the error in the CI is a bootstrapping problem, when upgrading the setuptools installation from source. The first time egg_info runs (via build_meta) in an environment that comes with an old version setuptools pre-installed, it will read the previous .dist-info/entry-points.txt and try to import egg_info.warn_depends_obsolete, resulting in error.

To avoid this error, the new commit will simply leave a stub behind which can then be removed in future versions.

[abravalheri]

@jaraco would you be OK with these removals or should we postpone them?

I also have #3951 open to remove old py*compat modules.

[jaraco]

LGTM. Thanks!

[jaraco]

This code is maintained upstream in jaraco/skeleton. I'm not sure what it even means to have matrix.python and matrix.dev in this section. Probably these lines simply need to be removed upstream. But that still doesn't address the concern that building against the default Python causes problems for Setuptools. Probably this change deserves a comment linking to a bug as to why it's here, because by pinning a version, it creates cruft that someone will have to revisit in the future (maybe just link to the comment).