bpf: struct sock is declared twice in bpf_sk_storage header

struct sock has been declared twice, therefore remove the duplicate.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210325070602.858024-1-wanjiabing@vivo.com

include/net/bpf_sk_storage.h

@@ -27,7 +27,6 @@ struct bpf_local_storage_elem;
 struct bpf_sk_storage_diag;
 struct sk_buff;
 struct nlattr;
-struct sock;
 
 #ifdef CONFIG_BPF_SYSCALL
 int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk);