The essl_to_hlsl and essl_to_glsl projects were exactly the same so it
doesn't make sense to keep both.

BUG=angleproject:981

Change-Id: Ibf034a71e94ba5002f9c40ac87720bf0de74ae18
Reviewed-on: https://chromium-review.googlesource.com/266872Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>