There is no need for 4 meeting channels, especially now that
we allow meetings to happen in team channels.
Let's remove #openstack-meeting-4 by moving the few meetings
still happening there to other available meeting channels.
Assuming it gets the required +1s, this change will be merged
Thursday, Mar 19 at 15utc (after the Glance meeting completes)
Once this merges, we can retire #openstack-meeting-4.
Change-Id: I96890de13083c09bdd677bf44b6eee535e6fde20