Add GLES 3.1 and 3.2 headers.

Remove GLES 3.0 extension headers and entry point files.

Change-Id: Icaa444efa52f3b9d1497189da92bc364545a6e3a
Reviewed-on: https://chromium-review.googlesource.com/299172Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>