Refactoring RbacUtils

Remove RbacUtils class and move all functionality to RbacUtilsMixin.

Story: 2002604
Task: 22223

Change-Id: If476be8fd3df78b28669ca940ebeb288af534899
diff --git a/patrole_tempest_plugin/rbac_rule_validation.py b/patrole_tempest_plugin/rbac_rule_validation.py
index 5dd4731..8236df9 100644
--- a/patrole_tempest_plugin/rbac_rule_validation.py
+++ b/patrole_tempest_plugin/rbac_rule_validation.py
@@ -345,7 +345,7 @@
             roles.append(CONF.patrole.rbac_test_role)
 
     # Adding implied roles
-    roles = test_obj.rbac_utils.get_all_needed_roles(roles)
+    roles = test_obj.get_all_needed_roles(roles)
 
     # Test RBAC against custom requirements. Otherwise use oslo.policy.
     if CONF.patrole.test_custom_requirements: