Change skip controller use branching_enabled

The before action to check that the advanced branching features are
enabled has been changed to use the Page#branching_enabled method, which
checks the group and the environment variable.

Author: thomasiles

app/controllers/pages/secondary_skip_controller.rb

@@ -79,7 +79,9 @@ def delete_secondary_skip_input_params
   end
 
   def ensure_branch_routing_feature_enabled
-    raise ActionController::RoutingError, "branch_routing feature not enabled" unless Settings.features.branch_routing
+    return if branching_enabled
+
+    raise ActionController::RoutingError, "branch_routing feature not enabled"
   end
 
   def ensure_page_has_skip_condition