Remove unused private API action methods

path_parts lost its last caller in 1602d2e, when feature names began
coming from the route; disallow_unregistered_groups? in fa80cc3, when
its caller switched to `return if allow_unregistered_groups?`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: dpep

lib/flipper/api/action.rb

@@ -289,12 +289,6 @@ def request_method_name
         end
       end
 
-      # Private: split request path by "/"
-      # Example: "features/feature_name" => ['features', 'feature_name']
-      def path_parts
-        @request.path.split('/')
-      end
-
       def valid_request_method?
         VALID_REQUEST_METHOD_NAMES.include?(request_method_name)
       end

lib/flipper/api/v1/actions/groups_gate.rb

@@ -44,10 +44,6 @@ def allow_unregistered_groups?
             allow_unregistered_groups && allow_unregistered_groups == 'true'
           end
 
-          def disallow_unregistered_groups?
-            !allow_unregistered_groups?
-          end
-
           def group_name
             @group_name ||= string_param('name')
           end