Remove deprecated 'forbid_global_implied_dsr' feature flag

'forbid_global_implied_dsr' feature flag was added for Mitaka
and older branches which are not supported now.

Devstack already removed this feature flag setting
- Ia1eb87d68a6265d8541cb87a88523246885e5a8a

This commit removes this from tempest.

Change-Id: I5422e33867a6038e8a4782dbdc639434a3c2b4b6

releasenotes/notes/removal-deprecated-config-options-3db535b979fe3509.yaml

@@ -0,0 +1,8 @@
+---
+upgrade:
+  - |
+    Below config options or feature flags were deprecated for removal.
+    It's time to remove them as all supported stable branches are
+    good to handle them.
+
+    * ``[identity-feature-enabled].forbid_global_implied_dsr``

tempest/api/identity/admin/v3/test_roles.py

@@ -338,14 +338,13 @@ class RolesV3TestJSON(base.BaseIdentityV3AdminTest):
         # domain role to a global one
         self._create_implied_role(domain_role1['id'], self.role['id'])
 
-        if CONF.identity_feature_enabled.forbid_global_implied_dsr:
-            # The contrary is not true: we can't create an inference rule
-            # from a global role to a domain role
-            self.assertRaises(
-                lib_exc.Forbidden,
-                self.roles_client.create_role_inference_rule,
-                self.role['id'],
-                domain_role1['id'])
+        # The contrary is not true: we can't create an inference rule
+        # from a global role to a domain role
+        self.assertRaises(
+            lib_exc.Forbidden,
+            self.roles_client.create_role_inference_rule,
+            self.role['id'],
+            domain_role1['id'])
 
     @decorators.idempotent_id('3859df7e-5b78-4e4d-b10e-214c8953842a')
     def test_assignments_for_domain_roles(self):

tempest/config.py

@@ -229,17 +229,6 @@ IdentityFeatureGroup = [
                      "Empty list indicates all extensions are disabled. "
                      "To get the list of extensions run: "
                      "'openstack extension list --identity'"),
-    # TODO(rodrigods): This is a feature flag for bug 1590578 which is fixed
-    # in Newton and Ocata. This option can be removed after Mitaka is end of
-    # life.
-    cfg.BoolOpt('forbid_global_implied_dsr',
-                default=False,
-                help='Does the environment forbid global roles implying '
-                     'domain specific ones?',
-                deprecated_for_removal=True,
-                deprecated_reason="This feature flag was introduced to "
-                                  "support testing of old OpenStack versions, "
-                                  "which are not supported anymore"),
     cfg.BoolOpt('domain_specific_drivers',
                 default=False,
                 help='Are domain specific drivers enabled? '