We do not need to explicitly cleanup ssh sessions anymore.
With libpam-systemd >= 230-2, ssh-session-cleanup.service is no longer necessary because when "UsePAM yes" in /etc/ssh/sshd_config (which is the default), SSH sessions are cleaned up automatically when ssh-server is shutdown or the system is rebooted.
See: https://salsa.debian.org/ssh-team/openssh/-/commit/556ee3d2d433dc70512003667398f0979b0940a9