Revert of MediaCaptureFromElement: add support for audio captureStream(). (patchset #6 id:760001 of )

Reason for revert:
The layout tests added are flakily crashing on various bots,

Original issue's description:
> MediaCaptureFromElement: add support for audio captureStream().
> This CL extends support for capturing the audio part of
> a <video> or <audio> tags ( "capture" here means creating
> a MediaStream out of the HTMLElement)
> It introduces an HtmlAudioCapturerSource is-a AudioCapturerSource
> wrapped into an ExternalMediaStreamAudioSource to produce data
> towards the audio track.
> HtmlAudioCapturerSource also plugs into the
> WebMediaPlayer's WebAudioSourceProviderImpl to get
> a copy of the audio being rendered.
> Unit tests are added, and the existing LayouTests
> revamped (and split into several files for clarity).
> BUG=569976, 575492
> TEST= run chromium with
>  --enable-blink-features=MediaCaptureFromVideo
>  against e.g.
> Committed:
> Cr-Commit-Position: refs/heads/master@{#395205},,,,,
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=569976, 575492

Cr-Commit-Position: refs/heads/master@{#395298}
15 files changed