KNF
RSA_NULL used to be a compile option allowing the RSA interfaces to be
compiled-in, with nonfunctional code, to be able to cope with the RSA
patent.

However, we don't use this option, and the RSA patent has expired more than 10
years ago, so just drop this piece.
remove unused dynamic_cmd_defns_empty structure.

ok miod@ deraadt@ guenther@
Remove RSA_memory_lock(). This undocumented function sort-of serializes your
RSA components to memory and clears them, but there is no unserializing
function, so its usefulness is close to zero.

A grep through the ports tree sources show that it is only present in ports
embedding their own openssl copy, and never used otherwise.

ok jsing@