Updating ffmpeg deprecated functions TODO.

webrtc:8745 is closed and it was about unblocking the Chromium roll,
webrtc:9352 is the new bug to keep track of the removal of ffmpeg
deprecated functions.

Bug: webrtc:9352
Change-Id: I2818dba804f3d611d4df80559a635e7cf1ee5338
No-Try: True
TBR: phoglund@webrtc.org
Reviewed-on: https://webrtc-review.googlesource.com/80882
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23506}

modules/video_coding/BUILD.gn

@@ -280,7 +280,7 @@ rtc_static_library("webrtc_h264") {
       "//third_party/openh264:encoder",
     ]
 
-    # TODO(bugs.webrtc.org/8745): stop using av_lockmgr_register
+    # TODO(bugs.webrtc.org/9352): Stop using ffmpeg deprecated functions.
     if (!is_win) {
       cflags = [ "-Wno-deprecated-declarations" ]
     }