Revert of Mustash: Ensure surfaces submitted to Mus by WM and embedders contain Surfaces with embeded content.

ui/aura/mus/window_port_mus.h

Index: ui/aura/mus/window_port_mus.h
diff --git a/ui/aura/mus/window_port_mus.h b/ui/aura/mus/window_port_mus.h
index f687f42b04f99e1b550a7262efcdad7edb7369d2..fd598d0f5a2bc09238754b8555e13b94fa66e0b8 100644
--- a/ui/aura/mus/window_port_mus.h
+++ b/ui/aura/mus/window_port_mus.h
@@ -26,7 +26,6 @@
 
 namespace aura {
 
-class ClientSurfaceEmbedder;
 class PropertyConverter;
 class SurfaceIdHandler;
 class Window;
@@ -244,9 +243,6 @@
 
   Window* window_ = nullptr;
 
-  // Used when this window is embedding a client.
-  std::unique_ptr<ClientSurfaceEmbedder> client_surface_embedder;
-
   ServerChangeIdType next_server_change_id_ = 0;
   ServerChanges server_changes_;