Remove process thread checker from BWE.

R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1898723002 .

Cr-Commit-Position: refs/heads/master@{#12408}
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.cc b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.cc
index a13f6df..5bd0627 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.cc
+++ b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.cc
@@ -92,7 +92,6 @@
     RTC_DCHECK(observer_);
     LOG(LS_INFO) << "RemoteBitrateEstimatorAbsSendTime: Instantiating.";
     network_thread_.DetachFromThread();
-    process_thread_.DetachFromThread();
 }
 
 void RemoteBitrateEstimatorAbsSendTime::ComputeClusters(
@@ -359,7 +358,6 @@
 
 void RemoteBitrateEstimatorAbsSendTime::OnRttUpdate(int64_t avg_rtt_ms,
                                                     int64_t max_rtt_ms) {
-  RTC_DCHECK(process_thread_.CalledOnValidThread());
   rtc::CritScope lock(&crit_);
   remote_rate_.SetRtt(avg_rtt_ms);
 }
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h
index 2d92b29..e56f4ba 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h
+++ b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_abs_send_time.h
@@ -130,7 +130,6 @@
   int64_t first_packet_time_ms_;
   int64_t last_update_ms_;
 
-  rtc::ThreadChecker process_thread_;
   rtc::CriticalSection crit_;
   Ssrcs ssrcs_ GUARDED_BY(&crit_);
   AimdRateControl remote_rate_ GUARDED_BY(&crit_);