Ussuri-only: Remove TripleO job

... because TipleO project has decided to EOL Ussuri[1].

[1] https://review.opendev.org/c/openstack/releases/+/834049

Change-Id: Icb6cbda77f2a971af0ae6c430190eddf0aee03a9

.zuul.yaml

@@ -5,24 +5,3 @@
       - puppet-openstack-integration-jobs-scenario003
       - puppet-openstack-beaker-jobs
       - release-notes-jobs-python3
-    check:
-      jobs:
-        - puppet-horizon-tripleo-standalone
-    gate:
-      jobs:
-        - puppet-horizon-tripleo-standalone
-
-- job:
-    name: puppet-horizon-tripleo-standalone
-    parent: tripleo-puppet-ci-centos-8-standalone
-    description: |
-      TripleO standalone Job running Horizon specific Tempest tests.
-    vars:
-      build_container_images: true
-      featureset_override:
-        run_tempest: false
-        tempest_services:
-          - horizon
-        tempest_test_whitelist:
-          - 'horizon'
-        use_os_tempest: true