Remove the VoiceEngineObserver callback interface.

voice_engine/include/voe_errors.h

 /*
  *  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.
  */
 
@@ skipping 61 matching lines @@
 #define VE_APM_ERROR 8097
 #define VE_RUNTIME_PLAY_WARNING 8098
 #define VE_RUNTIME_REC_WARNING 8099
 #define VE_NOT_PLAYING 8100
 #define VE_SOCKETS_NOT_INITED 8101
 #define VE_CANNOT_GET_SOCKET_INFO 8102
 #define VE_INVALID_MULTICAST_ADDRESS 8103
 #define VE_DESTINATION_NOT_INITED 8104
 #define VE_RECEIVE_SOCKETS_CONFLICT 8105
 #define VE_SEND_SOCKETS_CONFLICT 8106
-#define VE_TYPING_NOISE_WARNING 8107
+// 8107 is not used
 #define VE_NOISE_WARNING 8109
 #define VE_CANNOT_GET_SEND_CODEC 8110
 #define VE_CANNOT_GET_REC_CODEC 8111
 #define VE_ALREADY_INITED 8112
 #define VE_CANNOT_SET_SECONDARY_SEND_CODEC 8113
 #define VE_CANNOT_GET_SECONDARY_SEND_CODEC 8114
 #define VE_CANNOT_REMOVE_SECONDARY_SEND_CODEC 8115
-#define VE_TYPING_NOISE_OFF_WARNING 8116
+// 8116 is not used
 
 // Errors causing limited functionality
 #define VE_RTCP_SOCKET_ERROR 9001
 #define VE_MIC_VOL_ERROR 9002
 #define VE_SPEAKER_VOL_ERROR 9003
 #define VE_CANNOT_ACCESS_MIC_VOL 9004
 #define VE_CANNOT_ACCESS_SPEAKER_VOL 9005
 #define VE_GET_MIC_VOL_ERROR 9006
 #define VE_GET_SPEAKER_VOL_ERROR 9007
 #define VE_THREAD_RTCP_ERROR 9008
@@ skipping 55 matching lines @@
 #define VE_CANNOT_STOP_PLAYOUT 10031
 #define VE_CANNOT_INIT_CHANNEL 10032
 #define VE_RECV_SOCKET_ERROR 10033
 #define VE_SOCKET_TRANSPORT_MODULE_ERROR 10034
 #define VE_AUDIO_CONF_MIX_MODULE_ERROR 10035
 
 // Warnings for other platforms (reserved range 8061-8080)
 #define VE_IGNORED_FUNCTION 8061
 
 #endif  //  VOICE_ENGINE_VOE_ERRORS_H_