As far as I can tell, every call site already populates this field, so
we can now remove it.
Bug: webrtc:8975
Change-Id: I58515dd16d4ad8bf8872077b67a67f6e92e7b542
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/171222
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30857}