AGC1: remove unused field trial WebRTC-UseLegacyDigitalGainApplier

Bug: webrtc:14685
Change-Id: I7c9e07c56f20bd9c4b8848787d0b6e4f9785af60
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/283764
Reviewed-by: Hanna Silen <silen@webrtc.org>
Commit-Queue: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38687}
diff --git a/modules/audio_processing/gain_control_impl.cc b/modules/audio_processing/gain_control_impl.cc
index 3fac1f7..edc49d1 100644
--- a/modules/audio_processing/gain_control_impl.cc
+++ b/modules/audio_processing/gain_control_impl.cc
@@ -39,12 +39,8 @@
   return -1;
 }
 
-// Checks whether the legacy digital gain application should be used.
-bool UseLegacyDigitalGainApplier() {
-  return field_trial::IsEnabled("WebRTC-UseLegacyDigitalGainApplier");
-}
-
-// Floating point variant of WebRtcAgc_Process.
+// Applies the sub-frame `gains` to all the bands in `out` and clamps the output
+// in the signed 16 bit range.
 void ApplyDigitalGain(const int32_t gains[11],
                       size_t num_bands,
                       float* const* out) {
@@ -97,7 +93,6 @@
 
 GainControlImpl::GainControlImpl()
     : data_dumper_(new ApmDataDumper(instance_counter_)),
-      use_legacy_gain_applier_(UseLegacyDigitalGainApplier()),
       mode_(kAdaptiveAnalog),
       minimum_capture_level_(0),
       maximum_capture_level_(255),
@@ -236,26 +231,9 @@
     }
   }
 
-  if (use_legacy_gain_applier_) {
-    for (size_t ch = 0; ch < mono_agcs_.size(); ++ch) {
-      int16_t split_band_data[AudioBuffer::kMaxNumBands]
-                             [AudioBuffer::kMaxSplitFrameLength];
-      int16_t* split_bands[AudioBuffer::kMaxNumBands] = {
-          split_band_data[0], split_band_data[1], split_band_data[2]};
-      audio->ExportSplitChannelData(ch, split_bands);
-
-      int err_process = WebRtcAgc_Process(
-          mono_agcs_[ch]->state, mono_agcs_[index_to_apply]->gains, split_bands,
-          audio->num_bands(), split_bands);
-      RTC_DCHECK_EQ(err_process, 0);
-
-      audio->ImportSplitChannelData(ch, split_bands);
-    }
-  } else {
-    for (size_t ch = 0; ch < mono_agcs_.size(); ++ch) {
-      ApplyDigitalGain(mono_agcs_[index_to_apply]->gains, audio->num_bands(),
-                       audio->split_bands(ch));
-    }
+  for (size_t ch = 0; ch < mono_agcs_.size(); ++ch) {
+    ApplyDigitalGain(mono_agcs_[index_to_apply]->gains, audio->num_bands(),
+                     audio->split_bands(ch));
   }
 
   RTC_DCHECK_LT(0ul, *num_proc_channels_);
diff --git a/modules/audio_processing/gain_control_impl.h b/modules/audio_processing/gain_control_impl.h
index b65d697..8aea8f2 100644
--- a/modules/audio_processing/gain_control_impl.h
+++ b/modules/audio_processing/gain_control_impl.h
@@ -68,7 +68,6 @@
 
   std::unique_ptr<ApmDataDumper> data_dumper_;
 
-  const bool use_legacy_gain_applier_;
   Mode mode_;
   int minimum_capture_level_;
   int maximum_capture_level_;