Convert CNG into C++ and remove it from AudioDecoder

webrtc/modules/audio_coding/codecs/cng/cng_helpfuns.h

Index: webrtc/modules/audio_coding/codecs/cng/cng_helpfuns.h
diff --git a/webrtc/modules/audio_coding/codecs/cng/cng_helpfuns.h b/webrtc/modules/audio_coding/codecs/cng/cng_helpfuns.h
deleted file mode 100644
index a553a7615e693bba7021970573ae8bf9d5bf2f39..0000000000000000000000000000000000000000
--- a/webrtc/modules/audio_coding/codecs/cng/cng_helpfuns.h
+++ /dev/null
@@ -1,25 +0,0 @@
-/*
- *  Copyright (c) 2011 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.
- */
-#ifndef WEBRTC_MODULES_AUDIO_CODING_CODECS_CNG_CNG_HELPFUNS_H_
-#define WEBRTC_MODULES_AUDIO_CODING_CODECS_CNG_CNG_HELPFUNS_H_
-
-#include "webrtc/typedefs.h"
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-void WebRtcCng_K2a16(int16_t* k, int useOrder, int16_t* a);
-
-#ifdef __cplusplus
-}
-#endif
-
-#endif  // WEBRTC_MODULES_AUDIO_CODING_CODECS_CNG_CNG_HELPFUNS_H_