ASTC HDR is a superset of ASTC LDR, so always use HDR enums
on supported platforms because there is no such difference in OpenGL ES.

Bug: angleproject:2634, angleproject:5672
Change-Id: I19a3212bcb949aa9cdeb682ab000aa03125f04a9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2848509Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Le Hoang Quyen <le.hoang.q@gmail.com>
Commit-Queue: Alexey Knyazev <lexa.knyazev@gmail.com>