Also delete vulkan.hpp that we don't use, and vulkan_fuchsia_extras that
have since then been upstreamed.
Also updates the fuchsia external import code to use the non-temp
extension.
Bug: dawn:221
Change-Id: I23e1bfedc5a18731be1e58d0bae1bddf6b0f45fa
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/71601
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Loko Kung <lokokung@google.com>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>