Introduce a new NIR pass called nir_remove_outputs which works on
lowered I/O intrinsics and can remove any output varying or sysval.
This is meant to replace custom solutions in drivers,
such as radv_remove_varyings and similar.
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33928>
