The ub18-libc6, ub18-python-dbus, ub18-pygobject and ub18-pyatspi packages are no longer consumed by any docker image, so remove them along with the patch files that only they referenced. Also switch the remaining ub18-python-psutil and ub18-coreutils packages off launchpad.net source URLs in favour of snapshot.ubuntu.com. Differential Revision: https://phabricator.services.mozilla.com/D309271