Remove backwards compatibilty header for Optional

rtc_base/optional.h

Index: rtc_base/optional.h
diff --git a/rtc_base/optional.h b/rtc_base/optional.h
deleted file mode 100644
index 04294dc4522cc85676ec7acefd971da77b9339c8..0000000000000000000000000000000000000000
--- a/rtc_base/optional.h
+++ /dev/null
@@ -1,19 +0,0 @@
-/*
- *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-// This header is for backwards compatibility only, and will be removed soon.
-// Include webrtc/api/optional.h instead.
-
-#ifndef RTC_BASE_OPTIONAL_H_
-#define RTC_BASE_OPTIONAL_H_
-
-#include "api/optional.h"
-
-#endif  // RTC_BASE_OPTIONAL_H_