core: drop redundant logging about notification messages

      Before:
May 12 17:11:22 tomegun-x2402 systemd[1]: systemd-udevd.service: Got notification message for unit.
May 12 17:11:22 tomegun-x2402 systemd[1]: systemd-udevd.service: Got notification message from PID 195 (READY=1)
May 12 17:11:22 tomegun-x2402 systemd[1]: systemd-udevd.service: Ggot READY=1

After:
May 12 17:11:22 tomegun-x2402 systemd[1]: systemd-udevd.service: Got notification message from PID 195 (READY=1)