NetEq: Deprecate playout modes Fax, Off and Streaming

The playout modes other than Normal have not been reachable for a long
time, other than through tests. It is time to deprecate them.

The only meaningful use was that Fax mode was sometimes set from
tests, in order to avoid time-stretching operations (accelerate and
pre-emptive expand) from messing with the test results. With this CL,
a new config is added instead, which lets the user specify exactly
this: don't do time-stretching.

As a result of Fax and Off modes being removed, the following code
clean-up was done:
- Fold DecisionLogicNormal into DecisionLogic.
- Remove AudioRepetition and AlternativePlc operations, since they can
  no longer be reached.

Bug: webrtc:9421
Change-Id: I651458e9c1931a99f3b07e242817d303bac119df
Reviewed-on: https://webrtc-review.googlesource.com/84123
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Reviewed-by: Minyue Li <minyue@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23704}

modules/audio_coding/acm2/acm_receiver_unittest.cc

@@ -292,7 +292,7 @@ TEST_F(AcmReceiverTestOldApi, MAYBE_SampleRate) {
 class AcmReceiverTestFaxModeOldApi : public AcmReceiverTestOldApi {
  protected:
   AcmReceiverTestFaxModeOldApi() {
-    config_.neteq_config.playout_mode = kPlayoutFax;
+    config_.neteq_config.for_test_no_time_stretching = true;
   }
 
   void RunVerifyAudioFrame(RentACodec::CodecId codec_id) {
@@ -301,7 +301,7 @@ class AcmReceiverTestFaxModeOldApi : public AcmReceiverTestOldApi {
     // timestamp increments predictable; in normal mode, NetEq may decide to do
     // accelerate or pre-emptive expand operations after some time, offsetting
     // the timestamp.
-    EXPECT_EQ(kPlayoutFax, config_.neteq_config.playout_mode);
+    EXPECT_TRUE(config_.neteq_config.for_test_no_time_stretching);
 
     const RentACodec::CodecId kCodecId[] = {codec_id};
     AddSetOfCodecs(kCodecId);