Remove duplicate see also reference to BIO_s_mem.

Reviewed-by: NTim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3731)

doc/man7/bio.pod

@@ -70,14 +70,13 @@ L<BIO_push(3)>, L<BIO_read_ex(3)>,
 L<BIO_s_accept(3)>, L<BIO_s_bio(3)>,
 L<BIO_s_connect(3)>, L<BIO_s_fd(3)>,
 L<BIO_s_file(3)>, L<BIO_s_mem(3)>,
-L<BIO_s_mem(3)>,
 L<BIO_s_null(3)>, L<BIO_s_socket(3)>,
 L<BIO_set_callback(3)>,
 L<BIO_should_retry(3)>
 
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-Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
+Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
 
 Licensed under the OpenSSL license (the "License").  You may not use
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