Revert of Introduce ash mojo interface for lock screen action handlers

ash/tray_action/tray_action_observer.h

Index: ash/tray_action/tray_action_observer.h
diff --git a/ash/tray_action/tray_action_observer.h b/ash/tray_action/tray_action_observer.h
deleted file mode 100644
index 6a8faca408fa0e4c2d44e5c7ecbf27ea7184e605..0000000000000000000000000000000000000000
--- a/ash/tray_action/tray_action_observer.h
+++ /dev/null
@@ -1,22 +0,0 @@
-// Copyright 2017 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.
-
-#ifndef ASH_TRAY_ACTION_TRAY_ACTION_OBSERVER_H_
-#define ASH_TRAY_ACTION_TRAY_ACTION_OBSERVER_H_
-
-#include "ash/public/interfaces/tray_action.mojom.h"
-
-namespace ash {
-
-class TrayActionObserver {
- public:
-  virtual ~TrayActionObserver() {}
-
-  // Called when action handler state changes.
-  virtual void OnLockScreenNoteStateChanged(mojom::TrayActionState state) = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_TRAY_ACTION_TRAY_ACTION_OBSERVER_H_