Remove WindowTreeClientDelegate::GetCaptureClient() and WindowTreeClient::GetCaptureClient().

ui/aura/mus/window_tree_client.h

Index: ui/aura/mus/window_tree_client.h
diff --git a/ui/aura/mus/window_tree_client.h b/ui/aura/mus/window_tree_client.h
index cd62cfc90761b823d93436b2a9bb8d217b8dd32a..3b49d204a1c78e564ce15368c9372615d2d399ce 100644
--- a/ui/aura/mus/window_tree_client.h
+++ b/ui/aura/mus/window_tree_client.h
@@ -65,10 +65,6 @@ class WindowTreeClientObserver;
 class WindowTreeClientTestObserver;
 class WindowTreeHostMus;
 
-namespace client {
-class CaptureClient;
-}
-
 using EventResultCallback = base::Callback<void(ui::mojom::EventResult)>;
 
 // Manages the connection with mus.
@@ -109,8 +105,6 @@ class AURA_EXPORT WindowTreeClient
   bool connected() const { return tree_ != nullptr; }
   ClientSpecificId client_id() const { return client_id_; }
 
-  client::CaptureClient* GetCaptureClient();
-
   void SetCanFocus(Window* window, bool can_focus);
   void SetCanAcceptDrops(Id window_id, bool can_accept_drops);
   void SetCanAcceptEvents(Id window_id, bool can_accept_events);