Drop Python2 support

[DjLegolas]

As python2 is already at its EOF state, we can drop all of the support to it.

This PR will contain all of the changes to this end.

Plan:

• Remove __future__ imports
• Remove six dependency
• Remove future_builtins imports
• Change the way we perform string formats (maybe even move to f-strings only?)
• Make sure there are no sections that handles Py2 compatibilities
• Remove files coding header

If you know about any other things to change, please write.

[cas--]

If we are making wholesale changes, we can remove the following from all files:

# -*- coding: utf-8 -*-

[cas--]

Thanks for getting this work started.

Maybe look at using this: https://github.com/asottile/pyupgrade with --py36-plus since with can bump to >=3.6 (I know 3.6 EOL)

[bwitt]

+1 for using https://github.com/asottile/pyupgrade with --py36-plus ;
also suggest using https://github.com/asottile/reorder_python_imports with --py36-plus to fix up a few more things.

[DjLegolas]

Thanks for getting this work started.

Maybe look at using this: https://github.com/asottile/pyupgrade with --py36-plus since with can bump to >=3.6 (I know 3.6 EOL)

Do you want to add it permanently to the linting process?

[cas--]

What I would suggest is that this PR is wrapped up as is and we merge it. So things to finalise for this PR:

• remove urllib imports in PreferencesManager to pass the linting
• Any tests or reference to Python 2 use git grep -Ei "python.?2|py2[ 0-9]"

Then create a second PR that uses pyupgrade since that will be another huge changeset. Adding pyupgrade to pre-commit is helpful since if added as a pre-commit [manual] stage we can run it quickly with

pre-commit run pyupgrade -a

[cas--]

Best to remove this since we'll add it back when needed