mus: Remove some dead code from client-lib.

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

Index: components/mus/public/cpp/lib/window_tree_client_impl.cc
diff --git a/components/mus/public/cpp/lib/window_tree_client_impl.cc b/components/mus/public/cpp/lib/window_tree_client_impl.cc
index 163f1a35d31bdc70f3a169568e1c36a8d085bba5..5b1553f95f042ef6c560c46093b3fedaba4cf57e 100644
--- a/components/mus/public/cpp/lib/window_tree_client_impl.cc
+++ b/components/mus/public/cpp/lib/window_tree_client_impl.cc
@@ -655,13 +655,8 @@ void WindowTreeClientImpl::WmSetProperty(uint32_t change_id,
 ////////////////////////////////////////////////////////////////////////////////
 // WindowTreeClientImpl, private:
 
-void WindowTreeClientImpl::OnActionCompleted(bool success) {
-  if (!change_acked_callback_.is_null())
-    change_acked_callback_.Run();
-}
-
 mojo::Callback<void(bool)> WindowTreeClientImpl::ActionCompletedCallback() {
-  return [this](bool success) { OnActionCompleted(success); };
+  return [this](bool success) {};
 }
 
 }  // namespace mus