Stop testing on ubuntu-xenial

We can drop xenial support as bionic is stable, this also saves us some
CI resources.

Change-Id: Id0731f3f9eb35c1572bd038ffb92ddabf97906b3
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

.zuul.yaml

@@ -14,25 +14,17 @@
     parent: ansible-role-logrotate
     nodeset: ubuntu-bionic
 
-- job:
-    name: ansible-role-logrotate-ubuntu-xenial
-    parent: ansible-role-logrotate
-    nodeset: ubuntu-xenial
-
 - project:
     templates:
       - windmill-jobs-fedora-latest
       - windmill-jobs-bionic
-      - windmill-jobs-xenial
     check:
       jobs:
         - ansible-role-logrotate-fedora-latest
         - ansible-role-logrotate-ubuntu-bionic
-        - ansible-role-logrotate-ubuntu-xenial
         - tox-linters
     gate:
       jobs:
         - ansible-role-logrotate-fedora-latest
         - ansible-role-logrotate-ubuntu-bionic
-        - ansible-role-logrotate-ubuntu-xenial
         - tox-linters