Remove TripleO job

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

Change-Id: I7cdfa0b9e4b913d97f509d1f188ec7f337bfd05c

.zuul.yaml

@@ -4,22 +4,3 @@
       - puppet-openstack-module-unit-jobs
       - puppet-openstack-integration-jobs-all
       - release-notes-jobs-python3
-    check:
-      jobs:
-        - puppet-oslo-tripleo-standalone
-    gate:
-      jobs:
-        - puppet-oslo-tripleo-standalone
-
-- job:
-    name: puppet-oslo-tripleo-standalone
-    parent: tripleo-puppet-ci-centos-8-standalone
-    description: |
-      TripleO standalone Job running basic tests
-    vars:
-      build_container_images: true
-      featureset_override:
-        run_tempest: false
-        tempest_test_whitelist:
-          - 'tempest.scenario.test_server_basic_ops'
-        use_os_tempest: true