aura-mus: Remove dead code.

ui/aura/mus/mus_util.cc

Index: ui/aura/mus/mus_util.cc
diff --git a/ui/aura/mus/mus_util.cc b/ui/aura/mus/mus_util.cc
deleted file mode 100644
index f32e881ae6bdfd7e91fbf9725ce0d1740b0bece6..0000000000000000000000000000000000000000
--- a/ui/aura/mus/mus_util.cc
+++ /dev/null
@@ -1,30 +0,0 @@
-// Copyright 2015 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 "ui/aura/mus/mus_util.h"
-
-#include "ui/aura/window.h"
-#include "ui/base/class_property.h"
-
-namespace aura {
-namespace {
-
-// This code uses Set/GetNativeWindowProperty instead of Set/GetProperty to
-// avoid a dependency on mus.
-const char kMusWindowKey[] = "mus";
-
-}  // namespace
-
-ui::Window* GetMusWindow(Window* window) {
-  if (!window)
-    return nullptr;
-  return static_cast<ui::Window*>(
-      window->GetNativeWindowProperty(kMusWindowKey));
-}
-
-void SetMusWindow(Window* window, ui::Window* mus_window) {
-  window->SetNativeWindowProperty(kMusWindowKey, mus_window);
-}
-
-}  // namespace aura