Remove TripleO job

... because TripleO has switched to the independent release model and
its Xena release is not being created.

Change-Id: I7c566ff6621f98d833967c666ad6fa11c76504a8

.zuul.yaml

@@ -5,22 +5,3 @@
       - puppet-openstack-integration-jobs-all
       - puppet-openstack-litmus-jobs
       - release-notes-jobs-python3
-    check:
-      jobs:
-        - puppet-nova-tripleo-standalone
-    gate:
-      jobs:
-        - puppet-nova-tripleo-standalone
-
-- job:
-    name: puppet-nova-tripleo-standalone
-    parent: tripleo-puppet-ci-centos-8-standalone
-    description: |
-      TripleO standalone Job running Nova specific Tempest tests.
-    vars:
-      build_container_images: true
-      featureset_override:
-        run_tempest: false
-        tempest_test_whitelist:
-          - 'tempest.scenario.test_server_basic_ops'
-        use_os_tempest: true