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/graph/implementation/tests.rs

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