Remove an unnecessary call to Controller()->NoteHasBeenCanceled() in the
Cancel() method of WebTransport::DatagramUnderlyingSource. It has
already been called in UnderlyingSourceBase::cancelWrapper() so the call
was redundant.

BUG=1292387,1292463

Change-Id: Ie30f983e257bff3606f13268cabf8fde83d4543d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3428509
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/main@{#966047}