Removes unwanted mox and fixture files

Module ironic.openstack.commom.fixture.moxstubout and mockptch
are no longer needed, so the whole directory is removed by this
patch. mox is removed from test-requirements.txt because it is
no longer used in ironic unit test cases.

Change-Id: I6060546b565c096c3a602b22f28b5d84b8a03b24