Reuse @ack_2to3 in TestDevelop.test_2to3_user_mode

Feature/faster distribution hashcmp no remove

Remove the test, no longer relevant now that external links are no longer supported and PyPI no longer allows replacing packages.

Fixes #2107

Fixes https://github.com/pypa/setuptools/issues/2100

Fix typo

Stop recognizing files ending with .dist-info as dist

Tweak note about setup.cfg

Emit deprecation warning when 2to3 is used.

In the deprecation warning, acknowledge that it's only for projects that still require Python 2 support.

This note has gotten a bit out of date, since setup.py is no longer
required.

Filter lib2to3 (Pending)DeprecationWarning in testes