Fix CUSTOM_USER_MENU_TITLE non-translated string (#15575)

Marlin/src/lcd/menu/menu_main.cpp

@@ -171,11 +171,11 @@ void menu_main() {
 
   #if ENABLED(CUSTOM_USER_MENUS)
     #ifdef CUSTOM_USER_MENU_TITLE
-      #undef MSG_USER_MENU
+      SUBMENU_P(PSTR(CUSTOM_USER_MENU_TITLE), menu_user);
-      #define MSG_USER_MENU CUSTOM_USER_MENU_TITLE
+    #else
-    #endif
       SUBMENU(MSG_USER_MENU, menu_user);
     #endif
+  #endif
 
   #if ENABLED(ADVANCED_PAUSE_FEATURE)
     #if E_STEPPERS == 1 && DISABLED(FILAMENT_LOAD_UNLOAD_GCODES)