Revert "Merge #96844: nixos/nfsd: run rpc-statd as a normal user"

This reverts commit 42eebd7ade, reversing
changes made to b169bfc9e2.

This breaks nfs3.simple test and even current PR #97656 wouldn't fix it.
Therefore let's revert for now to unblock the channels.

nixos/modules/tasks/filesystems/nfs.nix

@@ -101,6 +101,13 @@ in
       };
 
     systemd.services.rpc-statd =
-      { restartTriggers = [ nfsConfFile ]; };
+      { restartTriggers = [ nfsConfFile ];
+
+        preStart =
+          ''
+            mkdir -p /var/lib/nfs/{sm,sm.bak}
+          '';
+      };
+
   };
 }