ITS#10214 Reduce library dependencies

HAMANO Tsukasarequested to merge
hamano/openldap:reduce_deps into master

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.

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