crypto: remove deprecated ECDH calls w/ OpenSSL 1.1

These are both no-ops in OpenSSL 1.1.0.

PR-URL: https://github.com/nodejs/node/pull/16130
Backport-PR-URL: https://github.com/nodejs/node/pull/18622


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