Point tails::jenkins::apt_proxy to the devel branch on lizard

… that is, drop its custom value for the tails_git_revision parameter in nodes.pp, once devel has auto/scripts/update-acng-config, that is once feature/5926-freezable-APT-repository is merged.

Parent Task: #5926 (closed)

Original created by @intrigeri on 11415 (Redmine)