Clean up a-r-r role for upgrade test removal
Clean up a-r-r role for upgrade test removal

In I473b4162e141e05692e89f0420ea74c745dfc9e5 we forgot
to remove the ansible-role-requirements.yml entry for
previous_rabbitmq_server, so we do it here.

Change-Id: I1e844b0bfa41296075221992472d9369242e22ee

openstack/openstack-ansible-rabbitmq_server,openstack/openstack-ansible-rabbitmq_server