ASTC HDR formats are not enabled, and it's unlikely we'll have a need
for them, so remove them to detect attempted uses and declutter the
code a bit.

Bug: b/150130101
Change-Id: Ice39945dea4c0aeca027bf533253ae1915cb1170
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/46228
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>