backups: backup NixOS uid, gid mappings

Now that service uid, gid mappings are included in the backups, along
with the service data dirs, we can remove 'chown -R' for
clightning and liquidd data dirs.

Note that we used 'chown -R' only for these two services, while this
approach would have been relevant for all services with data dirs.

modules/clightning.nix

@@ -111,7 +111,6 @@ in {
       requires = [ "bitcoind.service" ];
       after = [ "bitcoind.service" ];
       preStart = ''
-        chown -R '${cfg.user}:${cfg.group}' '${cfg.dataDir}'
         # The RPC socket has to be removed otherwise we might have stale sockets
         rm -f ${cfg.networkDir}/lightning-rpc
         install -m 640 ${configFile} '${cfg.dataDir}/config'