Now that the new platform is in place, we can remove the old methods.
Must be landed after https://codereview.chromium.org/2697463003/

BUG=angleproject:1892
BUG=chromium:678870

Change-Id: Ia29a3b120cf3521fc0409019c2e64e4dbc6f460d
Reviewed-on: https://chromium-review.googlesource.com/441274
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>