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/neteq/include/neteq.h

@@ -74,13 +74,6 @@ struct NetEqLifetimeStatistics {
   uint64_t voice_concealed_samples = 0;
 };
 
-enum NetEqPlayoutMode {
-  kPlayoutOn,
-  kPlayoutOff,
-  kPlayoutFax,
-  kPlayoutStreaming
-};
-
 // This is the interface class for NetEq.
 class NetEq {
  public:
@@ -98,10 +91,10 @@ class NetEq {
     bool enable_post_decode_vad = false;
     size_t max_packets_in_buffer = 50;
     int max_delay_ms = 2000;
-    NetEqPlayoutMode playout_mode = kPlayoutOn;
     bool enable_fast_accelerate = false;
     bool enable_muted_state = false;
     absl::optional<AudioCodecPairId> codec_pair_id;
+    bool for_test_no_time_stretching = false;  // Use only for testing.
   };
 
   enum ReturnCodes { kOK = 0, kFail = -1, kNotImplemented = -2 };
@@ -209,16 +202,6 @@ class NetEq {
   // The packet buffer part of the delay is not updated during DTX/CNG periods.
   virtual int FilteredCurrentDelayMs() const = 0;
 
-  // Sets the playout mode to |mode|.
-  // Deprecated. Set the mode in the Config struct passed to the constructor.
-  // TODO(henrik.lundin) Delete.
-  virtual void SetPlayoutMode(NetEqPlayoutMode mode) = 0;
-
-  // Returns the current playout mode.
-  // Deprecated.
-  // TODO(henrik.lundin) Delete.
-  virtual NetEqPlayoutMode PlayoutMode() const = 0;
-
   // Writes the current network statistics to |stats|. The statistics are reset
   // after the call.
   virtual int NetworkStatistics(NetEqNetworkStatistics* stats) = 0;