GlobalMenu: remove shortcut for QuickSwitcher

The shortcut needs to work when there is no Global Menu, so it's also in QuickSwitcher.qml.
It can't be in both places, since that breaks it. So we remove it here.

BUG: 488212

src/qml/GlobalMenu.qml

@@ -88,7 +88,6 @@ Labs.MenuBar {
 
         Labs.MenuItem {
             text: i18nc("menu item that opens a UI element called the 'Quick Switcher', which offers a fast keyboard-based interface for switching in between chats.", "Open Quick Switcher")
-            shortcut: "Ctrl+K"
             onTriggered: quickSwitcher.open()
         }
     }