nir: Remove nir_alu_dest::write_mask

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24432>

src/compiler/spirv/spirv_to_nir.c

@@ -4067,7 +4067,6 @@ create_vec(struct vtn_builder *b, unsigned num_components, unsigned bit_size)
    nir_op op = nir_op_vec(num_components);
    nir_alu_instr *vec = nir_alu_instr_create(b->shader, op);
    nir_ssa_dest_init(&vec->instr, &vec->dest.dest, num_components, bit_size);
-   vec->dest.write_mask = (1 << num_components) - 1;
 
    return vec;
 }