Remove outdated Python2 code

[Rotzbua]

Change

• Remove outdated Python2 code
• Remove six package

[coveralls]

coverage: 87.805% (-0.04%) from 87.847% when pulling 1849bc4 on Rotzbua:remove_python2_code into 5e9ef5d on JohannesBuchner:master.

[JohannesBuchner]

imagehash had Python 2 support much longer than other packages, and it helped a number of users stuck on ancient systems that do not receive updates. I had PRs from several people over the years trying to remove it and calling it outdated.

Unfortunately it has basically become impossible to run CI against such old versions now. So I think we may have to go with the times and say goodbye to Python 2 support at this point and recommend the affected users to use old versions.

[JohannesBuchner]

Hi @Rotzbua, sorry for picking this up so late. I'd be happy to merge this, but I see that there is a conflict. Can you please fix it?

[Rotzbua]

I think it should first be clearly defined which python versions are supported 219 before migrations to a current modern python code are implemented.