bpo-37324: Remove ABC aliases from collections

[vstinner]

Remove deprecated aliases to Abstract Base Classes from the
collections module.

https://bugs.python.org/issue37324

[vstinner]

pip is broken by this change, causing test_venv to fail: https://bugs.python.org/issue37324#msg345906

[tirkarthi]

Vendored html5lib in pip was fixed upstream but needs a new release to fix thjs. See also discussion at #10596

[vstinner]

Oh. I wasn't aware of the previous attempt: #10596 there is a long discussion there.

Vendored html5lib in pip was fixed upstream but needs a new release to fix thjs. See also discussion at #10596

I also found some info about that: https://bugs.python.org/issue37324#msg345908

[vstinner]

It seems like jinja2 should be updated:

/home/vstinner/prog/python/master/env/lib/python3.9/site-packages/jinja2/utils.py:485: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3,and in 3.9 it will stop working
  from collections import MutableMapping

/home/vstinner/prog/python/master/env/lib/python3.9/site-packages/jinja2/runtime.py:318: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3,and in 3.9 it will stop working
  from collections import Mapping

/home/vstinner/prog/python/master/env/lib/python3.9/site-packages/jinja2/sandbox.py:82: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3,and in 3.9 it will stop working
  from collections import MutableSet, MutableMapping, MutableSequence

[vstinner]

This PR cannot be merged because it breaks the Python CI because of html5lib (used by pip): https://bugs.python.org/issue37324#msg348011 I prefer to close this PR right now. I will not be available next weeks, so I prefer to close the PR. I may reopen it later, once html5lib and pip are fixed.