remove unused import

Author: YoniFeng

src/trivial_impls.rs

@@ -10,7 +10,7 @@
 use crate::{Atom, StaticAtomSet};
 #[cfg(feature = "serde_support")]
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
-use std::borrow::{Borrow, Cow};
+use std::borrow::Cow;
 use std::fmt;
 
 impl<Static: StaticAtomSet> ::precomputed_hash::PrecomputedHash for Atom<Static> {