[applets/appmenu] Remove binding to checked property from MenuDelegate

It makes sense for ToolBar button in CompactRepresentation, because
background depends on it, but it is useless for custom AbstractButton
which has no special code handling this value.

applets/appmenu/package/contents/ui/main.qml

@@ -130,10 +130,7 @@ Item {
                 visible: text !== "" && model.activeActions.visible
 
                 menuIsOpen: Plasmoid.nativeInterface.currentIndex !== -1
-                onActivated: {
-                    Plasmoid.nativeInterface.trigger(this, index);
-                    checked = Qt.binding(() => Plasmoid.nativeInterface.currentIndex === index);
-                }
+                onActivated: Plasmoid.nativeInterface.trigger(this, index)
             }
         }
     }