Remove the preprocessor symbol WEBRTC_CODEC_AVT (it was always defined)

webrtc/modules/audio_coding/main/acm2/audio_coding_module_impl.cc

 /*
  *  Copyright (c) 2012 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 1112 matching lines @@
     case acm2::ACMCodecDB::kCNSWB:
       *codec_name = "CN";
       *sample_rate_hz = 32000;
       *channels = 1;
       break;
     case acm2::ACMCodecDB::kRED:
       *codec_name = "red";
       *sample_rate_hz = 8000;
       *channels = 1;
       break;
-#ifdef WEBRTC_CODEC_AVT
     case acm2::ACMCodecDB::kAVT:
       *codec_name = "telephone-event";
       *sample_rate_hz = 8000;
       *channels = 1;
       break;
-#endif
     default:
       FATAL() << "Codec type " << codec_type << " not supported.";
   }
   return true;
 }
 
 }  // namespace webrtc