The systemdunitdir option was split into systemdsystemunitdir and
systemduserunitdir before bluez5 was ever released, so this produced a
QA error and was ignored. There appears to be no reason to override the
inferred default, so replace it with an explicit --enable-systemd.
Signed-off-by: Peter A. Bigot <pab@pabigot.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>