network: do not serialize/deserialize routing policy rules

We already handle foreign routing policy rules correctly by the previous
commit. So, the serialization/deserialization of rules are not necessary
anymore.

src/network/networkd-manager.h

@@ -60,7 +60,6 @@ struct Manager {
 
         Set *rules;
         Set *rules_foreign;
-        Set *rules_saved;
 
         /* Manager stores routes without RTA_OIF attribute. */
         Set *routes;