Remove py33 from tox.ini until eventlet is ported

There is no point in trying to run the py33 unit tests until eventlet is
ported to Python 3. Meanwhile the expected failure means we get a bunch
of garbage and extra lag time when trying to run 'tox' before sending to
gerrit for review/CI checks.

Change-Id: I343e24e77e097a2249a7ace1903faeaed71d7393
Merge "Remove py33 from tox.ini until eventlet is ported"