ITS#10214 Reduce library dependencies
https://bugs.openldap.org/show_bug.cgi?id=10214
Note:
- The configure script checks for the presence of systemd/sd-daemon.h to determine the behavior of
--with-systemd=auto
. This header is not actually used. - sd-notify.h is a header-only library style. If it's better to split it into sd-notify.c, let's proceed with the split.