Use internal API for heat -> keystone communication

Continues work from https://review.opendev.org/676716

Change-Id: If0195c38034d404849bf2e8fca4629b2d38a2680
Closes-Bug: #1812864
Related-Bug: #1762754
Related-Bug: #1688331

ansible/roles/heat/templates/heat.conf.j2

@@ -72,9 +72,6 @@ password = {{ heat_keystone_password }}
 [ec2authtoken]
 auth_uri = {{ keystone_internal_url }}/v3
 
-[clients_keystone]
-auth_uri = {{ keystone_public_url }}
-
 [oslo_messaging_notifications]
 transport_url = {{ notify_transport_url }}
 {% if heat_enabled_notification_topics %}