nir/lower_wrmasks: drop support for I/O

nir_lower_wrmasks as-is is broken for semantic I/O, since semantic I/O is slot
based and nir_lower_wrmasks is purely byte-based. No drivers use it as such, and
no drivers should. Remove the support so people don't think it works. This came
up in !38482.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Marek Olšák <maraeo@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38533>

src/compiler/nir/nir_lower_wrmasks.c

@@ -62,9 +62,6 @@ static int
 value_src(nir_intrinsic_op intrinsic)
 {
    switch (intrinsic) {
-   case nir_intrinsic_store_output:
-   case nir_intrinsic_store_per_vertex_output:
-   case nir_intrinsic_store_per_view_output:
    case nir_intrinsic_store_ssbo:
    case nir_intrinsic_store_shared:
    case nir_intrinsic_store_global:
@@ -79,13 +76,10 @@ static int
 offset_src(nir_intrinsic_op intrinsic)
 {
    switch (intrinsic) {
-   case nir_intrinsic_store_output:
    case nir_intrinsic_store_shared:
    case nir_intrinsic_store_global:
    case nir_intrinsic_store_scratch:
       return 1;
-   case nir_intrinsic_store_per_vertex_output:
-   case nir_intrinsic_store_per_view_output:
    case nir_intrinsic_store_ssbo:
       return 2;
    default: