Replace OpenSSL AES with ctaes-based version
Backported from upstream PR https://github.com/bitcoin/bitcoin/pull/7689.
This is backported primarily to remove merge conflicts for a subsequent
backport, and also helps us towards removing OpenSSL. Its actual usage
in wallet encryption would be replaced by a more modern construction
before we make wallet encryption a supported feature, but for now this
does not affect anyone using the experimental feature.
2589b2fcc5