tcp: Remove a no-op eventhandler

It has done nothing since commit bc7d18ae72.  No functional change
intended.

Reviewed by:	tuexen
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D57101

sys/netinet/tcp_subr.c

@@ -1522,8 +1522,6 @@ tcp_init(void *arg __unused)
 #endif /* INET6 */
 
 	ISN_LOCK_INIT();
-	EVENTHANDLER_REGISTER(shutdown_pre_sync, tcp_fini, NULL,
-		SHUTDOWN_PRI_DEFAULT);
 	EVENTHANDLER_REGISTER(vm_lowmem, tcp_drain, NULL, LOWMEM_PRI_DEFAULT);
 	EVENTHANDLER_REGISTER(mbuf_lowmem, tcp_drain, NULL, LOWMEM_PRI_DEFAULT);
 
@@ -1629,12 +1627,6 @@ tcp_destroy(void *unused __unused)
 VNET_SYSUNINIT(tcp, SI_SUB_PROTO_DOMAIN, SI_ORDER_FOURTH, tcp_destroy, NULL);
 #endif
 
-void
-tcp_fini(void *xtp)
-{
-
-}
-
 /*
  * Fill in the IP and TCP headers for an outgoing packet, given the tcpcb.
  * tcp_template used to store this data in mbufs, but we now recopy it out

sys/netinet/tcp_var.h

@@ -1398,7 +1398,6 @@ struct tcpcb *
 void	 tcp_discardcb(struct tcpcb *);
 void	 tcp_twstart(struct tcpcb *);
 int	 tcp_ctloutput(struct socket *, struct sockopt *);
-void	 tcp_fini(void *);
 char	*tcp_log_addrs(struct in_conninfo *, struct tcphdr *, const void *,
 	    const void *);
 char	*tcp_log_vain(struct in_conninfo *, struct tcphdr *, const void *,