remove redundant imports

detects redundant imports that can be eliminated.

for #117772 :

In order to facilitate review and modification, split the checking code and
removing redundant imports code into two PR.

compiler/rustc_data_structures/src/fingerprint/tests.rs

@@ -1,5 +1,4 @@
 use super::*;
-use crate::stable_hasher::Hash64;
 
 // Check that `combine_commutative` is order independent.
 #[test]

compiler/rustc_data_structures/src/graph/implementation/tests.rs

@@ -1,5 +1,4 @@
 use crate::graph::implementation::*;
-use std::fmt::Debug;
 
 type TestGraph = Graph<&'static str, &'static str>;
 

compiler/rustc_data_structures/src/intern/tests.rs

@@ -1,5 +1,4 @@
 use super::*;
-use std::cmp::Ordering;
 
 #[derive(Debug)]
 struct S(u32);

compiler/rustc_data_structures/src/obligation_forest/tests.rs

@@ -1,7 +1,6 @@
 use super::*;
 
 use std::fmt;
-use std::marker::PhantomData;
 
 impl<'a> super::ForestObligation for &'a str {
     type CacheKey = &'a str;

compiler/rustc_data_structures/src/sip128/tests.rs

@@ -1,6 +1,6 @@
 use super::*;
 
-use std::hash::{Hash, Hasher};
+use std::hash::Hash;
 
 // Hash just the bytes of the slice, without length prefix
 struct Bytes<'a>(&'a [u8]);