glsl_type: Drop the glsl_get_array_instance C helper

It was added in bce6f99875 even though it's completely redundant with
glsl_array_type().

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>

src/compiler/nir/nir_split_per_member_structs.c

@@ -50,7 +50,7 @@ member_type(const struct glsl_type *type, unsigned index)
    if (glsl_type_is_array(type)) {
       const struct glsl_type *elem =
          member_type(glsl_get_array_element(type), index);
-      return glsl_get_array_instance(elem, glsl_get_length(type));
+      return glsl_array_type(elem, glsl_get_length(type));
    } else {
       assert(glsl_type_is_struct(type));
       assert(index < glsl_get_length(type));