Avoid _distutils_hack.remove_shim on Python >= 3.12

[abravalheri]

In #3952 we learned that _distutils_hack may cause problems in Python 3.12 when pip is imported.

Summary of changes

_distutils_hack should not be disabled on Python >= 3.12
In this PR we:

• Skip DistutilsMetaFinder.spec_for_pip on Python >= 3.12
• Make _distutils_hack.remove_shim private on Python >= 3.12
  • This was designed to work well in https://github.com/pypa/pip/blob/23.1.2/src/pip/_internal/locations/_distutils.py#L12-L15: an AttributeError would be raised and simply ignored by pip.

Closes #3661

Pull Request Checklist

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

[jaraco]

This whole module is private, so it's probably not necessary to mark it private, but also no problem if it is.

[abravalheri]

Thank you Jason. The renaming of the function was inspired by this piece of code in pip:

try:
    __import__("_distutils_hack").remove_shim()
except (ImportError, AttributeError):
    pass

Due to the rename the call would fail with an AttributeError that would be simply ignored. Without the renaming, there is some change of the importer being disable on Python >= 3.12.

[vstinner]

Thank you for the fix!