Remove outdated comment about macOS cusorUpdate

Change-Id: Ic270e9800b56e4fa1027245bebc4cd08a58abb3f
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
(cherry picked from commit a0675562eaab4193f68fb391c5ea824ecb8f9f89)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/platforms/cocoa/qnsview_mouse.mm

@@ -483,10 +483,6 @@ static const QPointingDevice *pointingDeviceFor(qint64 deviceID)
 
 - (void)cursorUpdate:(NSEvent *)theEvent
 {
-    // Note: We do not get this callback when moving from a subview that
-    // uses the legacy cursorRect API, so the cursor is reset to the arrow
-    // cursor. See rdar://34183708
-
     if (!NSApp.active)
         return;