Do not support loading modules from "deviceinfo_modules_initfs"

This variable will dissappear from the deviceinfo at some point: https://gitlab.com/postmarketOS/pmaports/-/merge_requests/4169 so after it does, it would not make much sense to keep its use around.

The only reason is backwards compatibility. So @craftyguy, you choose if you want to first deprecate it, mark this as draft, and then remove the code, or if you want to do it right away.