test: use mustNotCall() in test-stream2-objects

Use `common.mustNotCall()` in test-stream2-objects.js to confirm that
noop function is never invoked.

PR-URL: https://github.com/nodejs/node/pull/13249


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>