radv: Remove I/O variables after nir_lower_io.

They are not needed anymore.

Both NIR and RADV shader info can be fully deduced from I/O
intrinsics, so there is no need to keep the variables.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28506>

src/amd/vulkan/nir/radv_nir_lower_io.c

@@ -103,6 +103,8 @@ radv_nir_lower_io(struct radv_device *device, nir_shader *nir)
        */
       nir_recompute_io_bases(nir, nir_var_shader_in);
    }
+
+   NIR_PASS_V(nir, nir_remove_dead_variables, nir_var_shader_in | nir_var_shader_out, NULL);
 }
 
 /* IO slot layout for stages that aren't linked. */