Removes some dead code from WindowTreeClient

components/mus/public/cpp/lib/window_tree_client_impl.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/mus/public/cpp/lib/window_tree_client_impl.h"
 
 #include "base/bind.h"
 #include "components/mus/common/util.h"
 #include "components/mus/public/cpp/input_event_handler.h"
 #include "components/mus/public/cpp/lib/in_flight_change.h"
@@ skipping 710 matching lines @@
     result = window_manager_delegate_->OnWmSetProperty(window, name, &data);
     if (result) {
       // If the resulting bounds differ return false. Returning false ensures
       // the client applies the bounds we set below.
       window->SetSharedPropertyInternal(name, data.get());
     }
   }
   tree_->WmResponse(change_id, result);
 }
 
-////////////////////////////////////////////////////////////////////////////////
-// WindowTreeClientImpl, private:
-
-mojo::Callback<void(bool)> WindowTreeClientImpl::ActionCompletedCallback() {
-  return [this](bool success) {};
-}
-
 }  // namespace mus