It's undocumented and unused in the tree.  The idea seems to have
never gained much traction, and can be removed without breaking
ABI compatibility.
Reviewed-by: NAndy Polyakov <appro@openssl.org>
Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2800)