display parking system in system resolver and remove unnecessary test

src/resolvers/SystemResolvers.ts

@@ -78,5 +78,18 @@ export const SystemResolvers: Resolvers<ServerContext> = {
 
       return await system.shuttleRepository.getShuttles();
     },
+    parkingSystem: async (parent, _args, contextValue, _info) => {
+      const system = contextValue.findSystemById(parent.id);
+      if (!system) {
+        return null;
+      }
+
+      const parkingRepository = system.parkingRepository;
+      if (!parkingRepository) return null;
+
+      return {
+        systemId: parent.id,
+      };
+    },
   },
 }