Remove unnecessary usage of noqa

openstack.common.gettextutils._ is already listed under
import_exceptions so it doesn't need a noqa.  Patch
c178e567cb48d3bc67dcf06bcbb4c6a97df9f434 added the use of six.moves.mox
and used a noqa to make it pass hacking, instead of adding a noqa to
every line that uses this, just add six.moves.mox to import_exceptions

Change-Id: I912048c1222c22ee13a4dc2dc68dafe350907220
Merge "Remove unnecessary usage of noqa"