macOS: Simplify child window parenting in recreateWindowIfNeeded()

The logic for this should ideally be handled in setParent(), but
for now let's clean up the code a tiny bit.

Pick-to: 6.5
Change-Id: Id2370d6704625038ab6b4fa246dea5d1c037371c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -1505,9 +1505,7 @@ void QCocoaWindow::recreateWindowIfNeeded()
         }
     }
 
-    if (isEmbeddedView) {
-        // An embedded window doesn't have its own NSWindow.
-    } else if (parentWindow) {
+    if (parentCocoaWindow) {
         // Child windows have no NSWindow, re-parent to superview instead
         [parentCocoaWindow->m_view addSubview:m_view];
     }