test: refactor test-dgram-oob-buffer

* Change common.noop to common.mustNotCall() to verify callback is not
  invoked.
* Add destructuring assignment for clarity. Yeah, clarity. That's why.

PR-URL: https://github.com/nodejs/node/pull/13443


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>