tailscale: fix `tailscaled` not running as root
tailscale: fix `tailscaled` not running as root

Run `tailscaled` using a system daemon as it does not work as a non-root
user without `userspace-networking`.

Also, remove the broken warning relating to setting the search domain.
Manually adding the search domain to `networking.search` isn't necessary
to use only machine names to refer to other machines.

LnL7/nix-darwin