Add GLES 3.1 and 3.2 headers.

Remove GLES 3.0 extension headers and entry point files.

Re-land fixes double define from different style defines in libGLESv2.gypi and
other projects.

Change-Id: I6204dc767bd83b7aa7e4d6e2fa338b2ce7f304d8
Reviewed-on: https://chromium-review.googlesource.com/299401Tested-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>