Retire PowerVMStacker SIG: End Project Gating

The PowerVMStacker SIG has been inactive for ~5 years so the SIG and
its repositories should be retired. See [1] for further details.

[1] https://lists.openstack.org/archives/list/openstack-discuss@lists.openstack.org/thread/S2GYZGXYGFMHMQ5CWF5P52BRW2YU4TVV/

Change-Id: I1e1f56f2aec4b4f22d3be776e5a6f4c0f46f7e1a

zuul.d/projects.yaml

@@ -881,11 +881,8 @@
 - project:
     name: openstack/ceilometer-powervm
     templates:
-      - docs-on-readthedocs
+      - noop-jobs
       - official-openstack-repo-jobs
-      - publish-to-pypi
-    vars:
-      rtd_webhook_id: '44767'
 
 - project:
     name: openstack/ceilometermiddleware
@@ -2814,11 +2811,8 @@
 - project:
     name: openstack/networking-powervm
     templates:
-      - docs-on-readthedocs
+      - noop-jobs
       - official-openstack-repo-jobs
-      - publish-to-pypi
-    vars:
-      rtd_webhook_id: '44768'
 
 - project:
     name: openstack/networking-sfc
@@ -2918,11 +2912,8 @@
 - project:
     name: openstack/nova-powervm
     templates:
-      - docs-on-readthedocs
+      - noop-jobs
       - official-openstack-repo-jobs
-      - publish-to-pypi
-    vars:
-      rtd_webhook_id: '44764'
 
 - project:
     name: openstack/nova-specs