[arch-releng] ISO test builds are back

I took the time to fix up the ISO build process. ISOs should now build again nightly. I removed AIF and added Dave's arch-install-scripts. These are incomplete and undocumented, so any installation you do with those images right now is done manually. Everyone who still wants to use the images can get them from the releng server [1] or boot them via netboot [2]. [1] https://releng.archlinux.org/isos/ [2] https://releng.archlinux.org/pxeboot/