Retire training-labs repo

As there is no maintainer for training-labs repo, and no
response on retirement proposal[1], this commit officially
retire it.

Depends-On: https://review.opendev.org/c/openstack/project-config/+/817507

[1] http://lists.openstack.org/pipermail/openstack-discuss/2021-October/025586.html

Change-Id: Ied6d8eb0beb74e14255a6d7e27cbb8af74b20cba

reference/legacy.yaml

@@ -1958,6 +1958,15 @@ swift:
       repos:
         - openstack/swift-specs
 
+Technical Writing SIG:
+  irc-channel: openstack-doc
+  partial: yes
+  deliverables:
+    training-labs:
+      retired-on: 2021-11-10
+      repos:
+        - openstack/training-labs
+
 Telemetry:
   irc-channel: openstack-telemetry
   service: Telemetry service

reference/sigs-repos.yaml

@@ -82,8 +82,6 @@ Security:
   - repo: openstack/security-analysis
   - repo: openstack/security-doc
   - repo: openstack/security-specs
-Technical Writing:
-  - repo: openstack/training-labs
 Testing and Collaboration Tools:
   - repo: openstack/bugdaystats
   - repo: openstack/ci-log-processing