test: refactor test-dns-regress-6244.js

* Move from parallel to internet because it performs a DNS query
* Provide link to relevant issue in comments
* Remove unnecessary explicit no-op function

PR-URL: https://github.com/nodejs/node/pull/13058


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>