nir/opt_varying: remove assert for mesh shader crash

This assert is not true when mesh shader.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36596>

src/compiler/nir/nir_opt_varyings.c

@@ -5487,7 +5487,6 @@ nir_opt_varyings_bulk(nir_shader **shaders, uint32_t num_shaders, bool spirv,
 
    for (unsigned i = 0; i < num_shaders; i++) {
       nir_shader *nir = shaders[i];
-      assert(i == 0 || nir->info.stage > shaders[i - 1]->info.stage);
 
       /* Inter-shader code motion in nir_opt_varyings requires that each input
        * load is loaded only once when possible, so move all input loads