test: remove unnecessary use of common.PORT in addons test

Using port 0 to request an open port from the operating system is
sufficient in openssl-client-cert-engine/test.js.

PR-URL: https://github.com/nodejs/node/pull/17563


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>