Make fingerd execute from systemd `socket` unit

Add systemd units fingerd.socket and fingerd@.service, and remove configuration of inetd. All debian-derived systems run systemd these days, and inetd is usually not installed by default. This change makes the service run out of the box, without the need to install inetd.

(As a sidenote, I would suggest to make finger a dependency for fingerd, instead of a suggestion. The server is unable to function without the finger binary.)

Signed-off-by: Eugene Crosser crosser@average.org