crypto: clear some SSL_METHOD deprecation warnings

Fixing the rest will be rather involved. I think the cleanest option is
to deprecate the method string APIs which are weird to begin with.

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


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