Make a few cleanups:
- Remove python 2.7 stanza from setup.py
- Add requires on python >= 3.6 to setup.cfg so that pypi and pip
know about the requirement
- Remove obsolete sections from setup.cfg:
* Wheel is not needed for python 3 only repo
* Some other sections are obsolete
- Update classifiers
- Update requirements, no need for python_version anymore
Change-Id: I49f919ee7d8a23d4958328966a2b633a12bb7525
Updates requirements to math global-requirements file.
Also fixes pep8 errors caused by updated requirements.
Change-Id: I4ae0e29db03a4c92e85cf063f049f0d587bc1148
Closes-Bug: #1466123