remove obsolete tox environments
remove obsolete tox environments

We no longer need to support 3.4 and 3.5 is covered by the default
debug environment.

Change-Id: I1ca069ea14c619bf64101c1c84bd1b4c3a2d2691
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

openstack/debtcollector