(player_kill_idle): Don't kill hung player threads. That code was

flawed.  Firstly, when player_kill_idle() ran before the player thread
could react to being aborted by update or shutdown, player_kill_idle()
incorrectly diagnosed it as hung.  Secondly, terminating hung threads
leaks resources and can leave a stale play_lock behind.  It could
perhaps even corrupt game state.  It might salvage some scenarios, but
makes others worse.  Not worth it.

src/server/main.c

@@ -385,7 +385,6 @@ shutdwn(int sig)
 	empth_wakeup(p->proc);
     }
     empth_rwlock_wrlock(play_lock);
-    /* rely on player_kill_idle() for killing hung player threads */
     if (sig)
 	logerror("Server shutting down on signal %d", sig);
     else