Document that preferred VideoFrame constructor takes no RTP timestamp.

And update most internal calls to use it.

Bug: webrtc:5740, webrtc:9372
Change-Id: Ib57d4ebfa7b0729af6d22981a792f0fdadf8a13f
Reviewed-on: https://webrtc-review.googlesource.com/81743
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23567}

modules/video_coding/codecs/h264/h264_decoder_impl.cc

@@ -137,9 +137,8 @@ int H264DecoderImpl::AVGetBuffer2(
       total_size,
       AVFreeBuffer2,
       static_cast<void*>(new VideoFrame(frame_buffer,
-                                        0 /* timestamp */,
-                                        0 /* render_time_ms */,
-                                        kVideoRotation_0)),
+                                        kVideoRotation_0,
+                                        0 /* timestamp_us */)),
       0);
   RTC_CHECK(av_frame->buf[0]);
   return 0;