The GLSL emitted for these was invalid, and we don't need these
structs since they're only used as the store types of buffers, which
are handled elsewhere.
Change-Id: I17c15e408b5c36e9b895e5950528a6d02d1802a6
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/72381
Reviewed-by: Stephen White <senorblanco@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>