Remove backwards compatibilty header for ArrayView

BUG=webrtc:8205

Review-Url: https://codereview.webrtc.org/3010633002
Cr-Commit-Position: refs/heads/master@{#19884}

rtc_base/BUILD.gn

@@ -105,7 +105,6 @@ rtc_source_set("rtc_base_approved_generic") {
   deps = []
 
   sources = [
-    "array_view.h",
     "arraysize.h",
     "atomicops.h",
     "base64.cc",

rtc_base/array_view.h

@@ -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/array_view.h instead.
-
-#ifndef RTC_BASE_ARRAY_VIEW_H_
-#define RTC_BASE_ARRAY_VIEW_H_
-
-#include "api/array_view.h"
-
-#endif  // RTC_BASE_ARRAY_VIEW_H_