Delete method DecoderDatabase::RegisterPayload(...NetEqDecoder...)

Bug: webrtc:10185
Change-Id: I69ce40b1c7267b039cd1d2237c5d5bbae3a81875
Reviewed-on: https://webrtc-review.googlesource.com/c/116683
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26208}

modules/audio_coding/neteq/neteq_decoder_enum.cc

@@ -77,8 +77,6 @@ absl::optional<SdpAudioFormat> NetEqDecoderToSdpAudioFormat(NetEqDecoder nd) {
       return SdpAudioFormat("cn", 32000, 1);
     case NetEqDecoder::kDecoderCNGswb48kHz:
       return SdpAudioFormat("cn", 48000, 1);
-    case NetEqDecoder::kDecoderReplacementForTest:
-      return SdpAudioFormat("replacement", 48000, 1);
     default:
       return absl::nullopt;
   }