Remove the sudo permissions required for make_unattended by using xorriso instead

[e-minguez]

Turns out xorriso can not only recreate isos magically but also extract files from them xorriso -osirrox so https://github.com/suse-edge/misc/blob/main/slemicro/make_unattended.sh can be improved by removing the need for doing things dangerously as root.