Drop Python 2 support.

[auvipy]

Fixes #6230

[rpkilby]

• Update docs index.md and release-notes.md
• Update readme
• Replace six compat with Python 3 equivalent

[carltongibson]

Hi @auvipy. I think we're good to go given the ticket: we'll drop Py2 for 3.10.

Are you happy to make a good first pass at the code changes with this? (Or we can pull these changes into a bigger PR...?)

Thanks for making the start. It's 💃🏼

[carltongibson]

But we don’t run stable branches. We can’t merge this until we’re sure there won’t be more 3.9.x releases.

[carltongibson]

Can you pull them into one branch/PR please. (Separate commits for each stage are fine.)

[auvipy]

OK I will put all changes in this branch

[auvipy]

seems like I accidentally removed some working code in generic relations tests

[auvipy]

how to fix this?
============================= ERRORS ====================================
______ ERROR collecting tests/generic_relations/test_generic_relations.py ______
tests/generic_relations/test_generic_relations.py:11: in
class Tag(models.Model):
.tox/venvs/py34-django111/lib/python3.4/site-packages/django/db/models/base.py:319: in new
new_class._meta.apps.register_model(new_class._meta.app_label, new_class)
.tox/venvs/py34-django111/lib/python3.4/site-packages/django/apps/registry.py:224: in register_model
(model_name, app_label, app_models[model_name], model))
E RuntimeError: Conflicting 'tag' models in application 'generic_relations': <class 'tests.generic_relations.models.Tag'> and <class 'tests.generic_relations.test_generic_relations.Tag'>.

[auvipy]

what is the alternative of from django.utils.six.moves import reload_module?

[auvipy]

well, should we move the six import clean up to another PR? or the six compats should be kept for few more versions?

[carltongibson]

Closing in favour of #6615. Thanks for the input @auvipy