sctp: Remove unused declaration sctp_backlog_migrate()

Commit 61c9fed4 ("[SCTP]: A better solution to fix the race between sctp_peeloff()
and sctp_rcv().") removed the implementation but left declaration in place. Remove it.
Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://lore.kernel.org/r/20230809142323.9428-1-yuehaibing@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/sctp/sctp.h

@@ -148,8 +148,6 @@ void sctp_icmp_redirect(struct sock *, struct sctp_transport *,
 void sctp_icmp_proto_unreachable(struct sock *sk,
 				 struct sctp_association *asoc,
 				 struct sctp_transport *t);
-void sctp_backlog_migrate(struct sctp_association *assoc,
-			  struct sock *oldsk, struct sock *newsk);
 int sctp_transport_hashtable_init(void);
 void sctp_transport_hashtable_destroy(void);
 int sctp_hash_transport(struct sctp_transport *t);