CI: Drop zun jobs

Similar to https://review.opendev.org/c/openstack/kolla-ansible/+/959307

Change-Id: I6033521fc1fefe55f685914f823d58c96f68611a
Signed-off-by: Michal Nasiadka <[email protected]>

Author: mnasiadka

.zuul.d/ubuntu.yaml

@@ -31,8 +31,6 @@
             files: ^docker/proxysql/
         - kolla-ansible-ubuntu-bifrost:
             files: ^docker/bifrost/
-        - kolla-ansible-ubuntu-zun:
-            files: ^docker/|zun/
     check-arm64:
       jobs:
         - kolla-build-ubuntu-aarch64