Revert "Support VTTCue.positionAlign and lineAlign for WebVTT"

This reverts commit 2c1d466d78db6df8b4c9fbe37ac5af1cb135bf34.

Reason for revert: https://crbug.com/814710

Conflicts with https://chromium-review.googlesource.com/836576 resolved.

Original change's description:
> Support VTTCue.positionAlign and lineAlign for WebVTT
>
> Implement VTTCue.[positionAlign and lineAlign] for WebVTT
> Updated parsing logic
> Exposed DOM API's
> Updated Layout algorithm
> Updated test expected results
>
> Bug: 633690
> Change-Id: I49970c068c53b462243ba8c7f314261b0e6455ce
> Reviewed-on: https://chromium-review.googlesource.com/756142
> Commit-Queue: srirama chandra sekhar <srirama.m@samsung.com>
> Reviewed-by: srirama chandra sekhar <srirama.m@samsung.com>
> Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
> Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
> Reviewed-by: Fredrik Söderquist <fs@opera.com>
> Cr-Commit-Position: refs/heads/master@{#525659}

TBR=fs@opera.com,chrishtr@chromium.org,srirama.m@samsung.com,foolip@chromium.org,k2.nagaraju@samsung.com

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

Bug: 633690
Change-Id: Ib9f0b3dd1a4b679076ec55ec635337551f8b8806