test: remove known_issues/test-cluster-bind-privileged-port

The test was added to check for a bug in macOS Mojave, but it turns out
the issue is a macOS feature, not a bug.

Refs: https://github.com/nodejs/node/issues/21679#issuecomment-456589386
Fixes: https://github.com/nodejs/node/issues/21679

PR-URL: https://github.com/nodejs/node/pull/25649


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>