horizon does not uses django-registration

It was removed from the requirements since long, by
a47aa6fdc33ee29be886b45236e276a42a70b4df.

Just the files/rpms/horizon referencing it.

Change-Id: Ic1d413855e80a6f64d9d255f2d3a41f0925332c5
Merge "horizon does not uses django-registration"
Merge commit 'refs/changes/75/84475/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch