Revert "Capture from HTMLMediaElement: move LayoutTests to external/wpt"

This reverts commit 1674a85c4268a152fbf405b97e1c3082f8ec389f.

Reason for revert: results were unstable upstream: https://github.com/w3c/web-platform-tests/pull/6546 A provisional PR wasn't created for the CL so there's no way this could have been avoided.

Original change's description:
> Capture from HTMLMediaElement: move LayoutTests to external/wpt
> 
> This CL moves the three standard functionality LayoutTests for 
> mediacapture-fromelement to the external/wpt folder, adapting 
> them accordingly and adding the necessary webmfiles.
> 
> Also removes the HTMLMediaElementCapture-*.html expectations.
> 
> Bug: 619625
> Change-Id: If06df91ae918b5f0d3eacc597c88709a83227a82
> Reviewed-on: https://chromium-review.googlesource.com/566151
> Commit-Queue: Miguel Casas <mcasas@chromium.org>
> Reviewed-by: Emircan Uysaler <emircan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#486677}

TBR=mcasas@chromium.org,emircan@chromium.org

Change-Id: Id0c5e1a45f9d4e65929aede3a6f256eae3850a3e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 619625
Reviewed-on: https://chromium-review.googlesource.com/572087
Reviewed-by: Jeff Carpenter <jeffcarp@chromium.org>
Commit-Queue: Jeff Carpenter <jeffcarp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486829}