Remove py33 env from default tox list
Remove py33 env from default tox list

We no longer need to test on Python 3.3, so remove that environment from
the default list in the tox configuration.

Change-Id: Icb3f22224678f9dad5de610a40d43fbef47be7ef

openstack/oslo.concurrency,JioCloud/oslo.concurrency,varunarya10/oslo.concurrency