Remove unused RwLock

src/lib.rs

@@ -39,7 +39,7 @@ use std::marker::PhantomData;
 use std::panic::{RefUnwindSafe, UnwindSafe};
 use std::rc::Rc;
 use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, Mutex, RwLock, TryLockError};
+use std::sync::{Arc, Mutex, TryLockError};
 use std::task::{Poll, Waker};
 
 use async_lock::OnceCell;