Remove archive_policy configuration in ceilometer.conf

gnocchi have archive policy rule feature, which can control metric's
archive_policy. gnocchi also have a default archive policy rule which
is using low archive policy.

On the other hand, archive_policy is marked as deprecated and will be
removed in the feature in ceilometer[0].

So should better remove archive_policy ceilometer.conf.

[0] https://review.openstack.org/#/c/448586/

Change-Id: I0aa726f6420d628bda3fb4c4eba86b55fe1e2699
Closes-Bug: #1696038

ansible/roles/ceilometer/templates/ceilometer.conf.j2

@@ -64,5 +64,4 @@ interface = internal
 [dispatcher_gnocchi]
 filter_service_activity = False
 url = {{ internal_protocol }}://{{ kolla_internal_fqdn }}:{{ gnocchi_api_port }}
-archive_policy = low
 {% endif %}