Revert of Make DesktopWindowTreeHostX11::ShouldWindowContentsBeTransparent() relies on argb visual flag

ui/views/test/widget_test_mac.mm

Index: ui/views/test/widget_test_mac.mm
diff --git a/ui/views/test/widget_test_mac.mm b/ui/views/test/widget_test_mac.mm
index 91f824c2337534181cd218cd87c4abc36158cba2..ea9ed8eb7c104815fa805264363ba345de599432 100644
--- a/ui/views/test/widget_test_mac.mm
+++ b/ui/views/test/widget_test_mac.mm
@@ -89,10 +89,5 @@
   return NativeWidgetMac::GetBridgeForNativeWindow(widget->GetNativeWindow());
 }
 
-// static
-bool WidgetTest::IsNativeWindowTransparent(gfx::NativeWindow window) {
-  return ![window isOpaque];
-}
-
 }  // namespace test
 }  // namespace views