[NETFILTER]: nf_conntrack_proto_icmp: kill extern declaration in .c file

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/nf_conntrack_proto_icmp.c

@@ -128,7 +128,6 @@ static int icmp_new(struct nf_conn *conntrack,
 	return 1;
 }
 
-extern struct nf_conntrack_l3proto nf_conntrack_l3proto_ipv4;
 /* Returns conntrack if it dealt with ICMP, and filled in skb fields */
 static int
 icmp_error_message(struct sk_buff *skb,