units: drop After=systemd-networkd.service from systemd-resolved.service

This ordering existed since resolved was first created, but there should
not be any need to order the two services against each other, as
resolved should be able to pick up networkd DNS metadata either way (as
it works with inotify in /run).

Let's drop this hence, and not cargo-cult this to eternity

Also see: https://github.com/systemd/systemd/pull/22389#issuecomment-1045978403