Stop patching nsswitch.conf and make resolv.conf points to stub-resolv.conf on Arch...

Stop patching nsswitch.conf and make resolv.conf points to stub-resolv.conf on Arch Linux

The `nsswitch.conf` file that comes by default on Arch Linux is now fully systemd-resolved compatible.
Its `hosts:` line is now:
```
hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname
```
So, there is no need to patch this file when enabling systemd-resolved on Arch Linux anymore.

Also make `/etc/resolv.conf` points to the new dynamic `/run/systemd/resolve/stub-resolv.conf` rather than the older static `/usr/lib/systemd/resolv.conf`.