Delete nack_enabled flag in encoder configuration.

This is a followup to cl https://webrtc-review.googlesource.com/71380,
which reworked the way encoder resilience is done, and made the
nack_enabled flag unused.

Bug: webrtc:8830
Change-Id: I3de2508c97bc71e01c8f2232d16cd1f33e57fe4a
Reviewed-on: https://webrtc-review.googlesource.com/69986
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23080}

modules/video_coding/video_codec_initializer_unittest.cc

diff --git a/modules/video_coding/video_codec_initializer_unittest.cc b/modules/video_coding/video_codec_initializer_unittest.cc
index 2ef1159..104b149 100644
--- a/modules/video_coding/video_codec_initializer_unittest.cc
+++ b/modules/video_coding/video_codec_initializer_unittest.cc
@@ -39,7 +39,7 @@
 // TODO(sprang): Extend coverage to handle the rest of the codec initializer.
 class VideoCodecInitializerTest : public ::testing::Test {
  public:
-  VideoCodecInitializerTest() : nack_enabled_(false) {}
+  VideoCodecInitializerTest() {}
   virtual ~VideoCodecInitializerTest() {}
 
  protected:
@@ -76,7 +76,7 @@
     codec_out_ = VideoCodec();
     bitrate_allocator_out_.reset();
     temporal_layers_.clear();
-    if (!VideoCodecInitializer::SetupCodec(config_, streams_, nack_enabled_,
+    if (!VideoCodecInitializer::SetupCodec(config_, streams_,
                                            &codec_out_,
                                            &bitrate_allocator_out_)) {
       return false;
@@ -122,7 +122,6 @@
   // Input settings.
   VideoEncoderConfig config_;
   std::vector<VideoStream> streams_;
-  bool nack_enabled_;
 
   // Output.
   VideoCodec codec_out_;