Delete deprecated VP8Decoder::Create

Bug: webrtc:15791
Change-Id: Ic198706535da9f299735cd0a7bbf571cda643098
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/340461
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41837}
diff --git a/modules/video_coding/BUILD.gn b/modules/video_coding/BUILD.gn
index eec1e66..58a92d5 100644
--- a/modules/video_coding/BUILD.gn
+++ b/modules/video_coding/BUILD.gn
@@ -559,7 +559,6 @@
     "../../api:field_trials_view",
     "../../api:scoped_refptr",
     "../../api/environment",
-    "../../api/transport:field_trial_based_config",
     "../../api/units:time_delta",
     "../../api/units:timestamp",
     "../../api/video:encoded_image",
diff --git a/modules/video_coding/codecs/vp8/include/vp8.h b/modules/video_coding/codecs/vp8/include/vp8.h
index b03200a..cb49516 100644
--- a/modules/video_coding/codecs/vp8/include/vp8.h
+++ b/modules/video_coding/codecs/vp8/include/vp8.h
@@ -41,12 +41,6 @@
   static std::unique_ptr<VideoEncoder> Create(Settings settings);
 };
 
-// TODO: bugs.webrtc.org/15791 - Delete in favor of the CreateVp8Decoder below.
-class VP8Decoder {
- public:
-  [[deprecated]] static std::unique_ptr<VideoDecoder> Create();
-};
-
 std::unique_ptr<VideoDecoder> CreateVp8Decoder(const Environment& env);
 
 }  // namespace webrtc
diff --git a/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.cc b/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.cc
index 3466080..3eed384 100644
--- a/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.cc
+++ b/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.cc
@@ -21,7 +21,6 @@
 #include "api/environment/environment.h"
 #include "api/field_trials_view.h"
 #include "api/scoped_refptr.h"
-#include "api/transport/field_trial_based_config.h"
 #include "api/video/i420_buffer.h"
 #include "api/video/video_frame.h"
 #include "api/video/video_frame_buffer.h"
@@ -87,10 +86,6 @@
 
 }  // namespace
 
-std::unique_ptr<VideoDecoder> VP8Decoder::Create() {
-  return std::make_unique<LibvpxVp8Decoder>();
-}
-
 std::unique_ptr<VideoDecoder> CreateVp8Decoder(const Environment& env) {
   return std::make_unique<LibvpxVp8Decoder>(env);
 }
@@ -119,15 +114,10 @@
   rtc::ExpFilter smoother_;
 };
 
-LibvpxVp8Decoder::LibvpxVp8Decoder()
-    : LibvpxVp8Decoder(FieldTrialBasedConfig()) {}
-
 LibvpxVp8Decoder::LibvpxVp8Decoder(const Environment& env)
-    : LibvpxVp8Decoder(env.field_trials()) {}
-
-LibvpxVp8Decoder::LibvpxVp8Decoder(const FieldTrialsView& field_trials)
-    : use_postproc_(kIsArm ? field_trials.IsEnabled(kVp8PostProcArmFieldTrial)
-                           : true),
+    : use_postproc_(
+          kIsArm ? env.field_trials().IsEnabled(kVp8PostProcArmFieldTrial)
+                 : true),
       buffer_pool_(false, 300 /* max_number_of_buffers*/),
       decode_complete_callback_(NULL),
       inited_(false),
@@ -135,9 +125,9 @@
       last_frame_width_(0),
       last_frame_height_(0),
       key_frame_required_(true),
-      deblock_params_(use_postproc_
-                          ? GetPostProcParamsFromFieldTrialGroup(field_trials)
-                          : absl::nullopt),
+      deblock_params_(use_postproc_ ? GetPostProcParamsFromFieldTrialGroup(
+                                          env.field_trials())
+                                    : absl::nullopt),
       qp_smoother_(use_postproc_ ? new QpSmoother() : nullptr) {}
 
 LibvpxVp8Decoder::~LibvpxVp8Decoder() {
diff --git a/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.h b/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.h
index 8ed8e7c..c14a2b7 100644
--- a/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.h
+++ b/modules/video_coding/codecs/vp8/libvpx_vp8_decoder.h
@@ -28,9 +28,6 @@
 
 class LibvpxVp8Decoder : public VideoDecoder {
  public:
-  // TODO: bugs.webrtc.org/15791 - Delete default constructor when
-  // Environment is always propagated.
-  LibvpxVp8Decoder();
   explicit LibvpxVp8Decoder(const Environment& env);
   ~LibvpxVp8Decoder() override;
 
@@ -61,7 +58,7 @@
 
  private:
   class QpSmoother;
-  explicit LibvpxVp8Decoder(const FieldTrialsView& field_trials);
+
   int ReturnFrame(const vpx_image_t* img,
                   uint32_t timeStamp,
                   int qp,