Remove release notes readthedocs webhook job

This was found not to work, and prevents releases from being made.

The cause of the issue is that the trigger-readthedocs-webhook job (in
project-config) is marked as 'final', meaning that a non-trusted Zuul
config source can't override its variables. Instead, you're supposed to
use the trigger-readthedocs-webhook project template, but only one
instance of this can be instantiated by design.

Let's revert to manually updating the release notes for now.

Change-Id: I271c972c7fdde23085f3026137806bb1e3048e5e

doc/source/development/releases.rst

@@ -124,4 +124,11 @@ Post-release activites
 An email will be sent to the release-announce mailing list about the new
 release.
 
-The release notes and documentation are built automatically via a webhook.
+The documentation on readthedocs is built automatically via a webhook.
+
+.. TODO: Setup RTD integration for release notes. This was attempted
+         previously but had issues with getting the zuul job to execute
+         twice with different webhook IDs, and broke the release pipeline.
+
+The release notes need to be rebuilt manually since there is no readthedocs
+webhook integration for these yet.

zuul.d/project.yaml

@@ -31,22 +31,3 @@
         - kayobe-overcloud-upgrade-centos
         - kayobe-seed-centos
         - kayobe-seed-upgrade-centos
-
-    post:
-      jobs:
-        - trigger-readthedocs-webhook:
-            vars:
-              rtd_project_name: kayobe-release-notes
-              rtd_webhook_id: '74820'
-    pre-release:
-      jobs:
-        - trigger-readthedocs-webhook:
-            vars:
-              rtd_project_name: kayobe-release-notes
-              rtd_webhook_id: '74820'
-    release:
-      jobs:
-        - trigger-readthedocs-webhook:
-            vars:
-              rtd_project_name: kayobe-release-notes
-              rtd_webhook_id: '74820'