skmsg: Remove unused sk_psock_stop() declaration

It is not defined or used anywhere.
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210223184934.6054-10-xiyou.wangcong@gmail.com

include/linux/skmsg.h

@@ -400,7 +400,6 @@ static inline struct sk_psock *sk_psock_get(struct sock *sk)
 	return psock;
 }
 
-void sk_psock_stop(struct sock *sk, struct sk_psock *psock);
 void sk_psock_drop(struct sock *sk, struct sk_psock *psock);
 
 static inline void sk_psock_put(struct sock *sk, struct sk_psock *psock)