zuul: drop devstack-gate reference

Devstack jobs no longer depend on the devstack-gate project, which has
been retired

Change-Id: Id4721d419b22b6d6498d192e3f313629ad33ef69
(cherry picked from commit 3e2a0ffe4f)
(cherry picked from commit 70f7bba359)
(cherry picked from commit db4b92fce4)
(cherry picked from commit c1b19c850a)
(cherry picked from commit ac44a0e105)
(cherry picked from commit 5a6502673a)

.gitreview

@@ -2,4 +2,4 @@
 host=review.opendev.org
 port=29418
 project=openstack/devstack-plugin-container.git
-defaultbranch=stable/victoria
+defaultbranch=unmaintained/victoria

.zuul.yaml

@@ -7,7 +7,6 @@
     timeout: 4200
     required-projects:
       - openstack/devstack
-      - openstack/devstack-gate
       - openstack/devstack-plugin-container
     vars:
       devstack_localrc:
@@ -25,7 +24,6 @@
     timeout: 7200
     required-projects:
       - openstack/devstack
-      - openstack/devstack-gate
       - openstack/devstack-plugin-container
     vars:
       devstack_services: