Remove unused variable from delay based BWE.

BUG=None

Review-Url: https://codereview.webrtc.org/2432923003
Cr-Commit-Position: refs/heads/master@{#14739}

webrtc/modules/congestion_controller/delay_based_bwe.cc

diff --git a/webrtc/modules/congestion_controller/delay_based_bwe.cc b/webrtc/modules/congestion_controller/delay_based_bwe.cc
index 55d29fb..fb6ffd1 100644
--- a/webrtc/modules/congestion_controller/delay_based_bwe.cc
+++ b/webrtc/modules/congestion_controller/delay_based_bwe.cc
@@ -129,8 +129,6 @@
     result.updated = UpdateEstimate(info.arrival_time_ms, now_ms,
                                     &result.target_bitrate_bps);
   }
-  rtc::Optional<uint32_t> incoming_rate =
-      receiver_incoming_bitrate_.Rate(info.arrival_time_ms);
   if (!result.updated &&
       (last_update_ms_ == -1 ||
        now_ms - last_update_ms_ > rate_control_.GetFeedbackInterval())) {