Deprecation of //asus/zephyrus/ga402x/default.nix

Background: The asus-zephyrus-ga402x provides an attr-set with amdgpu and nvidia entries, to allow users to choose whether to enable only the AMD-GPU driver, or also enable the NVidia driver with (by default) Prime enabled.

However, this attr-set style seems to be broken by PR #1046, which exports modules as paths, instead. That change seems to cause an error of "value is a path while a set was expected".