Remove AudioEncoder methods SetMaxBitrate and SetMaxPayloadSize

And the corresponding ACM methods SetISACMaxRate and
SetISACMaxPayloadSize. They were only used in tests.

Review URL: https://codereview.webrtc.org/1311533010

Cr-Commit-Position: refs/heads/master@{#9903}

webrtc/modules/audio_coding/codecs/audio_encoder.cc

@@ -52,8 +52,4 @@ void AudioEncoder::SetProjectedPacketLossRate(double fraction) {}
 
 void AudioEncoder::SetTargetBitrate(int target_bps) {}
 
-void AudioEncoder::SetMaxBitrate(int max_bps) {}
-
-void AudioEncoder::SetMaxPayloadSize(int max_payload_size_bytes) {}
-
 }  // namespace webrtc