3D texture implementation has already been done. It's time to remove
the UnsafeAPI toggle for it.
Bug: dawn:547
Change-Id: Ic9e0930d7906ee5274b9e412ebacb2574744b2b3
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/56480
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Yunchao He <yunchao.he@intel.com>