Remove workaround for old heat-tempest-plugin

Since 2.1.0, heat-tempest-plugin skips the scenario tests which
require voumes when cinder is not available.

Depends-on: https://review.opendev.org/853864
Change-Id: Ie701acd483dfb2247db329a149652bb63d288021

fixtures/scenario003.pp

@@ -81,9 +81,7 @@ class { 'openstack_integration::tempest':
   trove          => $trove_enabled,
   mistral        => true,
   horizon        => true,
-  # NOTE(tkajinam): The scenario job we enable requires cinder, which is not
-  #                 enabled in this scenario.
-  heat           => false,
+  heat           => true,
   magnum         => true,
   neutron_driver => 'ovn',
 }