QSystemTrayIcon: remove unused deprecated call to QAction::associatedWidgets()

This call was added in bcaff2b06f but
does not seem to be necessary. So just remove it.

Task-number: QTBUG-104857
Pick-to: 6.4 6.3 6.2
Change-Id: I2068bd10c6de211dd31f09ff978e8b8ba9cb70db
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

src/widgets/util/qsystemtrayicon.cpp

@@ -701,7 +701,6 @@ void QSystemTrayIconPrivate::addPlatformMenu(QMenu *menu) const
     // be higher than 3 levels.
     const auto actions = menu->actions();
     for (QAction *action : actions) {
-        QList<QWidget *> associatedWidgets = action->associatedWidgets();
         if (action->menu())
             addPlatformMenu(action->menu());
     }