Revert "ContextMenu: Allow plugins submenus to react to Shift modifiers"
This reverts commit ce3c2435. The apidox of setParentWidget says: Set the parent widget for any dialogs being shown. This should normally be your mainwindow, not a popup menu, so that it still exists even after the popup is closed (e.g. error message from KRun) and so that QAction::setStatusTip can find a statusbar, too. CCBUG: 425997