Remove Git commit message checks

Per the discussion in [1], we are removing the git commit message
hacking checks.  These cause issues with things like Gerrit reverts
and aren't that important to rigidly enforce.

[1]: http://lists.openstack.org/pipermail/openstack-dev/2014-December/052519.html

Change-Id: I601bb2eca0288f85597d3070abb855078eb1f29c