GitLab

Cleans up some more remnants from our fork of TtsController/Platform
from Chrome.

  - Remove VoicesChangedDelegate support, as we don't use this or need
    it.
  - Remove 'copied from chrome' comment as we are pretty thoroughly
    forked now.
  - Remove more code related to the tts_extension pieces we don't
    support
  - Remove a chromeos only test that was never compiled anyways.

Bug: none
Test: unit test and manual
Change-Id: I410603b58dac41772442af31597be7dda78be898
Reviewed-on: https://chromium-review.googlesource.com/1181174Reviewed-by: Alex Sakhartchouk <alexst@chromium.org>
Commit-Queue: Ryan Daum <rdaum@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584491}