move _generate_paths_by_default to where it is used

_generate_paths_by_default wasn't used in AD::Routing::UrlFor, so we
should be able to move it where it is used in AV::Routing

actionpack/lib/action_dispatch/routing/url_for.rb

@@ -184,12 +184,6 @@ module ActionDispatch
       def _routes_context
         self
       end
-
-      private
-
-        def _generate_paths_by_default
-          true
-        end
     end
   end
 end

actionview/lib/action_view/routing_url_for.rb

@@ -130,5 +130,11 @@ module ActionView
         controller.optimize_routes_generation? : super
     end
     protected :optimize_routes_generation?
+
+    private
+
+      def _generate_paths_by_default
+        true
+      end
   end
 end