Revert "Identify keyframe packets for FEC protection (#104)" (#105)

This reverts commit 19199df.

Author: taste1981

modules/rtp_rtcp/source/rtp_sender_video.cc

@@ -619,8 +619,6 @@ bool RTPSenderVideo::SendVideo(
 
     packet->set_allow_retransmission(allow_retransmission);
 
-    packet->set_is_key_frame(video_header.frame_type == VideoFrameType::kVideoFrameKey);
-
     // Put packetization finish timestamp into extension.
     if (packet->HasExtension<VideoTimingExtension>()) {
       packet->set_packetization_finish_time_ms(clock_->TimeInMilliseconds());