Retiring some old infrastructure

[kgilmer]

The old Debian apt repo and some arm64 build runners are being retired today. Anyone still using the old Debian apt repo (from before the previous 3.3 release) will see errors once the Debian host has been retired. Update the Regolith apt URL as specified on the install page to resolve the issue. All releases available in the old repository are available in the new so you should not need to upgrade your Regolith version when switching apt urls unless you choose to do so. (Edit: if you are on and wish to remain on 3.3, then you should set the repo component to v3.3 rather than main (see here for details)).

https://regolith-desktop.com/docs/using-regolith/install/