Retire Senlin project

Senlin project is in inactive list since 2024.1
- https://governance.openstack.org/tc/reference/emerging-technology-and-inactive-projects.html#current-inactive-projects

and there is no leader in 2024.2 cycle.
- https://etherpad.opendev.org/p/2024.2-leaderless

There is no response on last call for maintainers and retirement
notification:
- https://lists.openstack.org/archives/list/openstack-discuss@lists.openstack.org/thread/RYKD442DFHJ7CPLU5QKDTZQAAPNPFADP/

Seeing project inactivities and no maintainers for this project,
this commit propose to retire this project.

Change-Id: I619f7b662d21f218f8c99e09d2d8fd8b28f2d9c2

reference/legacy.yaml

@@ -2116,6 +2116,28 @@ Security:
       repos:
         - openstack/syntribos-payloads
 
+senlin:
+  irc-channel: senlin
+  service: Clustering service
+  mission: >
+    To implement clustering services and libraries for the management of groups
+    of homogeneous objects exposed by other OpenStack services.
+  url: https://wiki.openstack.org/wiki/Senlin
+  retired-on: 2024-05-10
+  deliverables:
+    senlin:
+      repos:
+        - openstack/senlin
+    python-senlinclient:
+      repos:
+        - openstack/python-senlinclient
+    senlin-dashboard:
+      repos:
+        - openstack/senlin-dashboard
+    senlin-tempest-plugin:
+      repos:
+        - openstack/senlin-tempest-plugin
+
 solum:
   mission: >
     To make cloud services easier to consume and integrate with your

reference/projects.yaml

@@ -2429,36 +2429,6 @@ sahara:
       release-management: none
       repos:
         - openstack/sahara-specs
-senlin:
-  ptl:
-    name: APPOINTMENT NEEDED
-    irc: No nick supplied
-    email: example@example.org
-  appointed:
-    - wallaby
-    - xena
-    - zed
-    - '2023.1'
-    - '2023.2'
-  irc-channel: senlin
-  service: Clustering service
-  mission: >
-    To implement clustering services and libraries for the management of groups
-    of homogeneous objects exposed by other OpenStack services.
-  url: https://wiki.openstack.org/wiki/Senlin
-  deliverables:
-    senlin:
-      repos:
-        - openstack/senlin
-    python-senlinclient:
-      repos:
-        - openstack/python-senlinclient
-    senlin-dashboard:
-      repos:
-        - openstack/senlin-dashboard
-    senlin-tempest-plugin:
-      repos:
-        - openstack/senlin-tempest-plugin
 skyline:
   ptl:
     name: Wenxiang Wu