Remove unused py33 tox env

Based on review comments in https://review.openstack.org/118771 it's
apparent that Cinder 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: I2bcc345bb62c0e08677fbf70b722b6a841650e53
Merge "Remove unused py33 tox env"