Remove redundant declarations in record_locl.h

This patch removes the prototype of function RECORD_LAYER_set_write_sequence from record_locl.h, since this function is not defined.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4051)