3D ASTC formats are not supported in Vulkan, sliced or not. The
non-sliced extension is already disabled, and this change disables the
sliced version.
Bug: angleproject:6038
Change-Id: I055838345ccb8ad77fe4c05e65dd8b10a8a4d36b
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2993459Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
