Drop local-charm-overlay.yaml.j2 and add ZAZA_FEATURE_BUG472=1

The overlay duplicates what is already in focal.yaml, and it is
causing the gate deployment to fail as follows:

ERROR cannot deploy bundle: the provided bundle has the
  following errors:
charm path in application "ceph-dashboard" does not exist:
  /ceph-dashboard.charm

Additionally this sets ZAZA_FEATURE_BUG472=1 for test runs as
deployments cannot get a public address otherwise:
  openstack-charmers/zaza#472

Depends-On: https://review.opendev.org/c/openstack/charm-ceph-dashboard/+/830967
Change-Id: I2b65cbb9c8d5c8b978b1474ac216a527bea09cb5

tox.ini

@@ -28,6 +28,7 @@ minversion = 3.2.0
 setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
          CHARM_DIR={envdir}
+         ZAZA_FEATURE_BUG472=1
 install_command =
   pip install {opts} {packages}
 commands = stestr run --slowest {posargs}