sysusers.d/systemd.conf is adding users for disabled functionalities. For example, if ./configure --disable-networkd is set, the user is still added.
Fixed in http://cgit.freedesktop.org/systemd/systemd/commit/?id=5a16bc264c.
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.