Small cleanup (util/mkdef.pl, crypto/bio/bss_log.c, include/openssl/ocsp.h)

BIO_s_log() is declared for everyone, so should return NULL when not
actually implemented.  Also, it had explicit platform limitations in
util/mkdef.pl that didn't correspond to what was actually in code.
While at it, a few other hard coded things that have lost their
relevance were removed.

include/openssl/ocsp.h had a few duplicate declarations.

Reviewed-by: Paul Yang <yang.yang@baishancloud.com>
(Merged from https://github.com/openssl/openssl/pull/7331)