This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove setup.* files, those are not needed for this repo.
- Cleanup */source/conf.py to remove now obsolete content.
- Remove install_command from tox.ini, the default is fine,
move constraints into deps
- Enable warnings for docs build
Change-Id: I07da37d6f15aefc7b2fa558a6ead7028d6c9c556
b64f07b80d