Switch to the Debian-packaged aufs kernel module

Originally created by @intrigeri on #11829 (Redmine)

It’s back into sid as aufs-dkms. It would be nicer than having to track upstream using a Git submodule, as we’re doing currently.

Feature Branch: feature/11829-aufs-from-Debian

Edited May 15, 2020 by intrigeri

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