nir: Remove old-school deref chain support

Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/nir/nir_lower_drawpixels.c

@@ -253,11 +253,6 @@ nir_lower_drawpixels(nir_shader *shader,
       .shader = shader,
    };
 
-   /* note that this pass already assumes texture/sampler derefs are already
-    * lowered to index
-    */
-   nir_assert_unlowered_derefs(shader, nir_lower_load_store_derefs);
-
    assert(shader->info.stage == MESA_SHADER_FRAGMENT);
 
    nir_foreach_function(function, shader) {