tcp: do not export tcp_peer_is_proven()

After commit 1fb6f159fd21 ("tcp: add tcp_conn_request"),
tcp_peer_is_proven() no longer needs to be exported.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_metrics.c

@@ -606,7 +606,6 @@ bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst,
 
 	return ret;
 }
-EXPORT_SYMBOL_GPL(tcp_peer_is_proven);
 
 void tcp_fetch_timewait_stamp(struct sock *sk, struct dst_entry *dst)
 {