Remove trusts_delegated_roles

This option's default value has changed since Newton.[1]

[1] https://github.com/openstack/heat/commit/aab01c00ff330d743fc15e97d7ae144eac5015bb

Change-Id: I981a59be716072aab40862b3e23bbb1fbd1d63fc

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

@@ -14,7 +14,6 @@ stack_domain_admin_password = {{ heat_domain_admin_password }}
 stack_user_domain_name = heat_user_domain
 
 deferred_auth_method = trusts
-trusts_delegated_roles = heat_stack_owner
 
 {% if service_name == 'heat-engine' %}
 num_engine_workers = {{ openstack_service_workers }}