With newer openstackdocstheme versions, many settings like
html_last_updated_fmt and latex are setup correctly and don't need to
setup in this repo anymore. We require a new enough version, so remove
the obsolete settings.
This repo now requires python 3, so remove python 2.7.x support.
Update hacking to current version supporting python 3.
Change-Id: I238eefeed275fe8115d0e253ca50d38086934b1e
48cd6edf98