remove re-export of parking_lot in util (#6435)

sync/src/light_sync/tests/test_net.rs

@@ -29,7 +29,7 @@ use light::client::Client as LightClient;
 use light::net::{LightProtocol, IoContext, Capabilities, Params as LightParams};
 use light::provider::LightProvider;
 use network::{NodeId, PeerId};
-use util::RwLock;
+use parking_lot::RwLock;
 
 use time::Duration;
 use light::cache::Cache;