Remove focal job for 2023.2

Neutron also flipped to python>=3.9 on all their repos this morningi[1]
which means we can't install neutron on focal at all. I'm not sure if
that's going to get reverted at this point, but even if it is, it's
going to take a while to undo. As noted in the comments and the
original commit[2] that added this job, it was intended to be removed
when we dropped focal from the test interface, which we have now done.

1: https://review.opendev.org/q/topic:bug%252F2017478
2: https://review.opendev.org/c/openstack/nova/+/861111

Change-Id: I5be638a702629e07ec9c88bd67bb9b7f1212f7fc

.zuul.yaml

@@ -658,15 +658,6 @@
             image_conversion:
               output_format: raw
 
-# TODO(gmann): As per the 2023.1 testing runtime, we need to run at least
-# one job on Focal. This job can be removed as per the future testing
-# runtime (whenever we drop the Ubuntu Focal testing).
-- job:
-    name: tempest-integrated-compute-ubuntu-focal
-    description: This is integrated compute job testing on Ubuntu Focal(20.04)
-    parent: tempest-integrated-compute
-    nodeset: openstack-single-node-focal
-
 # TODO(gmann): Remove this jobs once all the required services for intergrate
 # compute gate (Cinder, Glance, Neutron) by default enable scope and new
 # defaults which means all the nova jobs will be tested with new RBAC in
@@ -753,8 +744,6 @@
              - ^setup.cfg$
              - ^tools/.*$
              - ^tox.ini$
-        - tempest-integrated-compute-ubuntu-focal:
-            irrelevant-files: *policies-irrelevant-files
         - tempest-integrated-compute-enforce-scope-new-defaults:
             irrelevant-files: *policies-irrelevant-files
         - grenade-skip-level-always:
@@ -790,8 +779,6 @@
               - ^(?!nova/network/.*)(?!nova/virt/libvirt/vif.py).*$
         - tempest-integrated-compute:
            irrelevant-files: *policies-irrelevant-files
-        - tempest-integrated-compute-ubuntu-focal:
-            irrelevant-files: *policies-irrelevant-files
         - tempest-integrated-compute-enforce-scope-new-defaults:
             irrelevant-files: *policies-irrelevant-files
         - grenade-skip-level-always: