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/main/test/iSACTest.h

@@ -29,8 +29,6 @@ namespace webrtc {
 struct ACMTestISACConfig {
   int32_t currentRateBitPerSec;
   int16_t currentFrameSizeMsec;
-  uint32_t maxRateBitPerSec;
-  int16_t maxPayloadSizeByte;
   int16_t encodingMode;
   uint32_t initRateBitPerSec;
   int16_t initFrameSizeInMsec;