glsl: remove glsl ir optimisation loop from linker

glsl: remove glsl ir optimisation loop from linker

We no longer need to call this here and can depend on the glsl_to_nir
pass to call it and clean up anything it cannot handle. Everything
else can now depend on the nir optimisation passes.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22846>