In the Docker base image we are aiming not to install systemd by default, as it is not needed within that scope.  systemd-libs will remain however, but in that scenario pam_systemd serves no purpose either, and prevents us from removing pam as well.  Please move pam_systemd out of libs into either the main package or (if e.g. multilib is an issue) a separate pam-systemd package with a Recommends: thereon in the main package.