Removes deprecated path for sampling depth textures with
float/unfilterable-float. Attempting to do so now results in a
validation error.
Bug: dawn:1021
Change-Id: I112f45e7227ab1caaf0d6ed203194295e7022db2
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/61861
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Brandon Jones <bajones@chromium.org>