Remove old qt code

new round of removal following the report of @benj5378  .

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src/Gui/MenuManager.cpp

@@ -205,6 +205,11 @@ void MenuManager::setup(MenuItem* menuItems) const
 
     QMenuBar* menuBar = getMainWindow()->menuBar();
 
+    // clear() removes all the actions from the menu bar.
+    //Note: On macOS, menu items that have been merged to the system menu bar are not removed by this function.
+    //One way to handle this would be to remove the extra actions yourself.
+    //You can set the menu role on the different menus, so that you know ahead of time which menu items
+    //get merged and which do not. Then decide what to recreate or remove yourself. See also removeAction().
     menuBar->clear();
 
     QList<QAction*> actions = menuBar->actions();