Drop support for Python 2 code

[pombredanne]

We have a branch that has all the needed changes in ScanCode in aboutcode-org/scancode-toolkit#2167 by @Abhishek-Dev09 and that will need to be cherrypicked and filtered to keep the commoncode changes only.

@cco3 @tdruez FYI

[tdruez]

@pombredanne Make sure to merge #7 as well for Python 3.9 compatibility.

[pombredanne]

Completed. Thanks!