Remove unused py33 tox env

It's apparent that Nova is quite a ways from Py3K support, and
developers are not expected to run the py33 tox env. Rather than add
more envs for later Python interpreter versions which will be
equally broken, just remove it for now.

Change-Id: I885e6e8899f771cc52a2bf6282fd7bc1ed3083aa
Merge "Remove unused py33 tox env"