fix: unused clippy warning

Author: yannham

libdd-trace-utils/src/span/vec_map.rs

@@ -265,7 +265,6 @@ impl<K, V> Extend<(K, V)> for VecMap<K, V> {
 impl<K: Serialize + Eq + Hash, V: Serialize> Serialize for VecMap<K, V> {
     fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
         use serde::ser::SerializeMap;
-        use std::collections::HashMap;
 
         // We pre-compute the deduped map. If deduplication were done on the fly during
         // serialization, we couldn't provide a length up front to the serializer, and the current