Remove WebRTC-Bwe-AlrLimitedBackoff field trial.

This trial has been unused for some time, time to clean it up.

Bug: webrtc:10144
Change-Id: I2b1bd9ff0335efdc07f47a361878915f1be383a7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/267410
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37421}
diff --git a/modules/congestion_controller/goog_cc/delay_based_bwe.cc b/modules/congestion_controller/goog_cc/delay_based_bwe.cc
index 750c5c6..84cbcf5 100644
--- a/modules/congestion_controller/goog_cc/delay_based_bwe.cc
+++ b/modules/congestion_controller/goog_cc/delay_based_bwe.cc
@@ -59,8 +59,7 @@
     : updated(false),
       probe(false),
       target_bitrate(DataRate::Zero()),
-      recovered_from_overuse(false),
-      backoff_in_alr(false) {}
+      recovered_from_overuse(false) {}
 
 DelayBasedBwe::DelayBasedBwe(const FieldTrialsView* key_value_config,
                              RtcEventLog* event_log,
@@ -80,15 +79,10 @@
       uma_recorded_(false),
       rate_control_(key_value_config, /*send_side=*/true),
       prev_bitrate_(DataRate::Zero()),
-      has_once_detected_overuse_(false),
-      prev_state_(BandwidthUsage::kBwNormal),
-      alr_limited_backoff_enabled_(absl::StartsWith(
-          key_value_config->Lookup("WebRTC-Bwe-AlrLimitedBackoff"),
-          "Enabled")) {
+      prev_state_(BandwidthUsage::kBwNormal) {
   RTC_LOG(LS_INFO)
       << "Initialized DelayBasedBwe with separate audio overuse detection"
-      << separate_audio_.Parser()->Encode() << " and alr limited backoff "
-      << (alr_limited_backoff_enabled_ ? "enabled" : "disabled");
+      << separate_audio_.Parser()->Encode();
 }
 
 DelayBasedBwe::~DelayBasedBwe() {}
@@ -217,14 +211,8 @@
 
   // Currently overusing the bandwidth.
   if (active_delay_detector_->State() == BandwidthUsage::kBwOverusing) {
-    if (has_once_detected_overuse_ && in_alr && alr_limited_backoff_enabled_) {
-      if (rate_control_.TimeToReduceFurther(at_time, prev_bitrate_)) {
-        result.updated =
-            UpdateEstimate(at_time, prev_bitrate_, &result.target_bitrate);
-        result.backoff_in_alr = true;
-      }
-    } else if (acked_bitrate &&
-               rate_control_.TimeToReduceFurther(at_time, *acked_bitrate)) {
+    if (acked_bitrate &&
+        rate_control_.TimeToReduceFurther(at_time, *acked_bitrate)) {
       result.updated =
           UpdateEstimate(at_time, acked_bitrate, &result.target_bitrate);
     } else if (!acked_bitrate && rate_control_.ValidEstimate() &&
@@ -238,7 +226,6 @@
       result.probe = false;
       result.target_bitrate = rate_control_.LatestEstimate();
     }
-    has_once_detected_overuse_ = true;
   } else {
     if (probe_bitrate) {
       result.probe = true;
@@ -315,8 +302,4 @@
   return rate_control_.GetExpectedBandwidthPeriod();
 }
 
-void DelayBasedBwe::SetAlrLimitedBackoffExperiment(bool enabled) {
-  alr_limited_backoff_enabled_ = enabled;
-}
-
 }  // namespace webrtc
diff --git a/modules/congestion_controller/goog_cc/delay_based_bwe.h b/modules/congestion_controller/goog_cc/delay_based_bwe.h
index dd4f7d8..21dff357 100644
--- a/modules/congestion_controller/goog_cc/delay_based_bwe.h
+++ b/modules/congestion_controller/goog_cc/delay_based_bwe.h
@@ -55,7 +55,6 @@
     bool probe;
     DataRate target_bitrate = DataRate::Zero();
     bool recovered_from_overuse;
-    bool backoff_in_alr;
     BandwidthUsage delay_detector_state;
   };
 
@@ -80,7 +79,6 @@
   void SetStartBitrate(DataRate start_bitrate);
   void SetMinBitrate(DataRate min_bitrate);
   TimeDelta GetExpectedBwePeriod() const;
-  void SetAlrLimitedBackoffExperiment(bool enabled);
   DataRate TriggerOveruse(Timestamp at_time,
                           absl::optional<DataRate> link_capacity);
   DataRate last_estimate() const { return prev_bitrate_; }
@@ -126,9 +124,7 @@
   bool uma_recorded_;
   AimdRateControl rate_control_;
   DataRate prev_bitrate_;
-  bool has_once_detected_overuse_;
   BandwidthUsage prev_state_;
-  bool alr_limited_backoff_enabled_;
 };
 
 }  // namespace webrtc
diff --git a/modules/congestion_controller/goog_cc/goog_cc_network_control.cc b/modules/congestion_controller/goog_cc/goog_cc_network_control.cc
index 1a29327..bce1929 100644
--- a/modules/congestion_controller/goog_cc/goog_cc_network_control.cc
+++ b/modules/congestion_controller/goog_cc/goog_cc_network_control.cc
@@ -540,7 +540,6 @@
 
   NetworkControlUpdate update;
   bool recovered_from_overuse = false;
-  bool backoff_in_alr = false;
 
   DelayBasedBwe::Result result;
   result = delay_based_bwe_->IncomingPacketFeedbackVector(
@@ -562,18 +561,12 @@
   bandwidth_estimation_->UpdateLossBasedEstimator(report,
                                                   result.delay_detector_state);
   recovered_from_overuse = result.recovered_from_overuse;
-  backoff_in_alr = result.backoff_in_alr;
 
   if (recovered_from_overuse) {
     probe_controller_->SetAlrStartTimeMs(alr_start_time);
     auto probes = probe_controller_->RequestProbe(report.feedback_time.ms());
     update.probe_cluster_configs.insert(update.probe_cluster_configs.end(),
                                         probes.begin(), probes.end());
-  } else if (backoff_in_alr) {
-    // If we just backed off during ALR, request a new probe.
-    auto probes = probe_controller_->RequestProbe(report.feedback_time.ms());
-    update.probe_cluster_configs.insert(update.probe_cluster_configs.end(),
-                                        probes.begin(), probes.end());
   }
 
   // No valid RTT could be because send-side BWE isn't used, in which case