src: remove pre-openssl 1.0 legacy code

SSL_CIPHER and SSL_METHOD are always const with the version of openssl
that we support, no need to check OPENSSL_VERSION_NUMBER first.

PR-URL: https://github.com/nodejs/node/pull/6582


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>