crypto: make CipherBase 1.1.0-compatible

In OpenSSL 1.1.0, EVP_CIPHER_CTX must be heap-allocated. Once we're
heap-allocating them, there's no need in a separate initialised_ bit.
The presence of ctx_ is sufficient.

PR-URL: https://github.com/nodejs/node/pull/16130


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rod Vagg <rod@vagg.org>