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_span/src/source_map/tests.rs

@@ -1,7 +1,5 @@
 use super::*;
 
-use rustc_data_structures::sync::{FreezeLock, Lrc};
-
 fn init_source_map() -> SourceMap {
     let sm = SourceMap::new(FilePathMapping::empty());
     sm.new_source_file(PathBuf::from("blork.rs").into(), "first line.\nsecond line".to_string());