Cocoa: Disable malfunctioning updateScreens().

The current updateScreens() implementations deletes
QScreens and creates new ones. Deleting a QScreen hides
all its windows. The result is that Qt windows disappears
when applicationDidChangeScreenParameters is called.

Change-Id: I5870d025d2bbf36621817cb220a835d1a6b367dc
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>

src/plugins/platforms/cocoa/qcocoaapplicationdelegate.mm

@@ -344,12 +344,6 @@ static void cleanupCocoaApplicationDelegate()
 */
 }
 
-- (void)applicationDidChangeScreenParameters:(NSNotification *)notification
-{
-    Q_UNUSED(notification);
-    ((QCocoaIntegration*)QGuiApplicationPrivate::platformIntegration())->updateScreens();
-}
-
 - (void)setReflectionDelegate:(NSObject <NSApplicationDelegate> *)oldDelegate
 {
     [oldDelegate retain];