zuul: Stop testing against Tempest

Neither Tempest itself nor any of the service projects use OSC. As such,
there's no reason to run Tempest jobs here. It's simply a waste of
resources.

Change-Id: I74b0b196fe59e5e1462e3dadc659cf6680a53f80
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

.zuul.yaml

@@ -1,3 +1,4 @@
+---
 - job:
     name: osc-tox-unit-tips
     parent: openstack-tox
@@ -225,7 +226,6 @@
       - publish-openstack-docs-pti
       - check-requirements
       - release-notes-jobs-python3
-      - lib-forward-testing-python3
     check:
       jobs:
         - osc-build-image