crypto: fix mem {de}allocation in ExportChallenge
crypto: fix mem {de}allocation in ExportChallenge

Use correct deallocator for returned buffera.
Don't free internal structure via ASN1_STRING_data.
Deallocate NETSCAPE_SPKI.

PR-URL: https://github.com/nodejs/node/pull/2359
Reviewed-By: Fedor Indutny <e39d94bae70283f13d24c278e04952d6dad9384b@indutny.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node