This reverts commit 3f90035e2fac160d23309a96ef2cf465b29cebe4.

Reason for revert: The original problem was solved using another approach, and this CL just adds complexity with no purpose.

Original change's description:
> Implement DTMF [[ToneBuffer]] in the blink layer
>
> This CL makes the Blink layer keep a copy of the tone buffer
> and update it on insertDTMF and ontonechange events only; this
> makes it possible to expose the state of the tone buffer at the
> time the event is fired to the Javascript callback.
>
> It removes a queueing step inside the DTMF sender, because
> that queueing step destroyed the consistency.
>
> Bug: chromium:816475
> Change-Id: I5aa68396299a67d6cea1e8a17d364f553514c291
> Reviewed-on: https://chromium-review.googlesource.com/1213084
> Reviewed-by: Guido Urdaneta <guidou@chromium.org>
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Commit-Queue: Harald Alvestrand <hta@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#589910}

TBR=hta@chromium.org,haraken@chromium.org,hbos@chromium.org,guidou@chromium.org,foolip@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:816475
Change-Id: Iaee9fefa8a37e3c6c7256dacac0855f426601e0d