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_mir_transform/src/coverage/tests.rs

@@ -33,7 +33,7 @@ use rustc_data_structures::graph::WithSuccessors;
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::mir::*;
 use rustc_middle::ty;
-use rustc_span::{self, BytePos, Pos, Span, DUMMY_SP};
+use rustc_span::{BytePos, Pos, Span, DUMMY_SP};
 
 fn bcb(index: u32) -> BasicCoverageBlock {
     BasicCoverageBlock::from_u32(index)