Fix unused_imports

(cherry picked from commit a4c8748)

Author: cuviper

rayon-core/src/join/test.rs

@@ -1,7 +1,6 @@
 //! Tests for the join code.
 
-use crate::join::*;
-use crate::unwind;
+use super::*;
 use crate::ThreadPoolBuilder;
 use rand::distributions::Standard;
 use rand::{Rng, SeedableRng};