Revert "Reland "Allows FEC generation after pacer step.""

This reverts commit 19df870d924662e3b6efb86078d31a8e086b38b5.

Reason for revert: Downstream project failure

Original change's description:
> Reland "Allows FEC generation after pacer step."
> 
> This is a reland of 75fd127640bdf1729af6b4a25875e6d01f1570e0
> 
> Patchset 2 contains a fix. Old code can in factor call
> RtpRtcpImpl::FetchFec(). It should only be a noop since deferred fec
> is not supported there - we shouldn't crash.
> 
> Original change's description:
> > Allows FEC generation after pacer step.
> >
> > Split out from https://webrtc-review.googlesource.com/c/src/+/173708
> > This CL enables FEC packets to be generated as media packets are sent,
> > rather than generated, i.e. media packets are inserted into the fec
> > generator after the pacing stage rather than at packetization time.
> >
> > This may have some small impact of performance. FEC packets are
> > typically only generated when a new packet with a marker bit is added,
> > which means FEC packets protecting a frame will now be sent after all
> > of the media packets, rather than (potentially) interleaved with them.
> > Therefore this feature is currently behind a flag so we can examine the
> > impact. Once we are comfortable with the behavior we'll make it default
> > and remove the old code.
> >
> > Note that this change does not include the "protect all header
> > extensions" part of the original CL - that will be a follow-up.
> >
> > Bug: webrtc:11340
> > Change-Id: I3fe139c5d53968579b75b91e2612075451ff0f5d
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/177760
> > Commit-Queue: Erik Språng <sprang@webrtc.org>
> > Reviewed-by: Sebastian Jansson <srte@webrtc.org>
> > Cr-Commit-Position: refs/heads/master@{#31558}
> 
> Bug: webrtc:11340
> Change-Id: I2ea49ee87ee9ff409044e34a777a7dd0ae0a077f
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/177984
> Commit-Queue: Erik Språng <sprang@webrtc.org>
> Reviewed-by: Sebastian Jansson <srte@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#31613}

TBR=sprang@webrtc.org,srte@webrtc.org

Change-Id: I3b2b25898ce88b64c2322f68ef83f9f86ac2edb0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:11340
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/178563
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31614}

1 files changed, 0 insertions, 20 deletions

diff --git a/test/scenario/video_stream_unittest.cc b/test/scenario/video_stream_unittest.cc
index 873ef639ba..37afe1b1e7 100644
--- a/test/scenario/video_stream_unittest.cc
+++ b/test/scenario/video_stream_unittest.cc
@@ -9,7 +9,6 @@
  */
 #include <atomic>
 
-#include "test/field_trial.h"
 #include "test/gtest.h"
 #include "test/scenario/scenario.h"
 
@@ -171,25 +170,6 @@ TEST(VideoStreamTest, SendsFecWithFlexFec) {
   EXPECT_GT(video_stats.substreams.begin()->second.rtp_stats.fec.packets, 0u);
 }
 
-TEST(VideoStreamTest, SendsFecWithDeferredFlexFec) {
-  ScopedFieldTrials trial("WebRTC-DeferredFecGeneration/Enabled/");
-  Scenario s;
-  auto route =
-      s.CreateRoutes(s.CreateClient("caller", CallClientConfig()),
-                     {s.CreateSimulationNode([](NetworkSimulationConfig* c) {
-                       c->loss_rate = 0.1;
-                       c->delay = TimeDelta::Millis(100);
-                     })},
-                     s.CreateClient("callee", CallClientConfig()),
-                     {s.CreateSimulationNode(NetworkSimulationConfig())});
-  auto video = s.CreateVideoStream(route->forward(), [&](VideoStreamConfig* c) {
-    c->stream.use_flexfec = true;
-  });
-  s.RunFor(TimeDelta::Seconds(5));
-  VideoSendStream::Stats video_stats = video->send()->GetStats();
-  EXPECT_GT(video_stats.substreams.begin()->second.rtp_stats.fec.packets, 0u);
-}
-
 TEST(VideoStreamTest, ResolutionAdaptsToAvailableBandwidth) {
   // Declared before scenario to avoid use after free.
   std::atomic<size_t> num_qvga_frames_(0);