ac/nir/ngg: Remove unused vs_output struct.

Forgot to remove this when I refactored the code to use
ac_nir_prerast_out instead.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33218>

src/amd/common/nir/ac_nir_lower_ngg.c

@@ -24,12 +24,6 @@ typedef struct
    nir_variable *var;
 } reusable_nondeferred_variable;
 
-typedef struct
-{
-   gl_varying_slot slot;
-   nir_def *chan[4];
-} vs_output;
-
 typedef struct
 {
    const ac_nir_lower_ngg_options *options;