anv: use shader_info->var_copies_lowered

Instead of passing allow_copies as a parameter for brw_nir_optimize
(so manually doing that tracking).

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19338>

src/intel/compiler/brw_nir_rt.c

@@ -534,7 +534,7 @@ brw_nir_create_raygen_trampoline(const struct brw_compiler *compiler,
 
    NIR_PASS_V(nir, brw_nir_lower_cs_intrinsics);
 
-   brw_nir_optimize(nir, compiler, true, false);
+   brw_nir_optimize(nir, compiler, true);
 
    return nir;
 }