Revert "Define key_manager/api_class to a class full path"

Fix https://review.openstack.org/#/c/468252/ has been merged in cinder
and proper default configuration parameter is defined in puppet-cinder
so we don't need to set this parameter anymore.

This reverts commit f72ccac503.

Change-Id: I353b73ee351b5ef5c239d882cbc5477ae471391f
(cherry picked from commit 519399e7d6)

packstack/puppet/modules/packstack/manifests/cinder.pp

@@ -37,7 +37,6 @@ class packstack::cinder ()
       nova_catalog_admin_info => 'compute:nova:adminURL',
       service_workers         => hiera('CONFIG_SERVICE_WORKERS'),
       default_volume_type     => $default_volume_type,
-      keymgr_api_class        => 'castellan.key_manager.barbican_key_manager.BarbicanKeyManager',
     }
 
     class { '::cinder::scheduler': }