console-kit, systemd-login: Check for logind, not for systemd
It is possible to build systemd without logind, in which case sd_booted() wo
succeed. Check for /run/systemd/seats to test for logind instead, as
recommended by systemd upstream.
For details, see:
<https://mail.gnome.org/archives/desktop-devel-list/2013-March/msg00092.html
Drop the now unnecessary linking against libsystemd-daemon, and stop linking
the consolekit module to any systemd library.