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
(cherry picked from commit db1bf61805)

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()
         }
     }