Since the other backends no longer need it, move all of the
utility functions specific to SPIRV-Cross into the OpenGL backend.
This obviates the need for the DAWN_USE_SPIRV_CROSS define, so remove it.
Bug: dawn:1036
Change-Id: I67bb5a85dc128a6f343d09876046cf559395e05f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/61541
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Stephen White <senorblanco@chromium.org>
