[Merge] ~juliank/livecd-rootfs:deb822-sources into livecd-rootfs:ubuntu/master

[Julian Andres Klode]

Dropped the magic-proxy commit and the change to use_lp_archives or what it was called, so that it continues working with sources.list from live-build.

Patched the code to setup ubuntu.sources to also delete sources.list
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https://code.launchpad.net/~juliank/livecd-rootfs/+git/livecd-rootfs/+merge/458366
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