This reverts commit c7abc080.

Reason for revert: Might have broken Chromium Win10 composition due to validation changes.

Original change's description:
> Implement EGL_ANGLE_iosurface_client_buffer
> 
> BUG=angleproject:1649
> 
> Change-Id: I1e72c31d7c9497ad14039a8d3fb97317ab193cb2
> Reviewed-on: https://chromium-review.googlesource.com/559107
> Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> Reviewed-by: Geoff Lang <geofflang@chromium.org>
> Commit-Queue: Corentin Wallez <cwallez@chromium.org>

TBR=geofflang@chromium.org,cwallez@chromium.org

Change-Id: I605b710b6d76056d6276b09822cd6ddca277bfd0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: angleproject:1649
Reviewed-on: https://chromium-review.googlesource.com/822172Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>