This removes devstack-gate from the CI system and updates ACLS for the
repo in Gerrit to the openstack retired repo config. There are also
cleanups to nodepool elements and irc bots to remove references to
devstack-gate where we don't need them anymore.
Depends-On: https://review.opendev.org/c/openstack/governance/+/919629
Change-Id: I50ce4e5aa7001ba52bea78a65855278be68e61a5