Remove help message about ZeroMQ driver
Remove help message about ZeroMQ driver

ZeroMQ driver is deprecated, as per the Dublin 2018 PTG decision:
http://lists.openstack.org/pipermail/openstack-dev/2018-March/128055.html

Change-Id: Ia3d5fd1d2ccd57bf3b9f97172c09994bf5d44022

openstack/watcher,stackforge/watcher,openstack/watcher,stackforge/watcher