Remove mox3 requirement

mox3 is only used got py3 testing when converting tests from mox,
all OSC tests are new so we don't need it.

Change-Id: I2fae539e99143f91048c95d1e46cfbd7b0e9bdb0

Author: Dean Troyer

test-requirements.txt

@@ -4,7 +4,6 @@ coverage>=3.6
 discover
 fixtures>=0.3.14
 mock>=1.0
-mox3>=0.7.0
 sphinx>=1.1.2,<1.2
 testrepository>=0.0.17
 testtools>=0.9.32