Fix clippy::needless_borrow in the compiler

`x clippy compiler -Aclippy::all -Wclippy::needless_borrow --fix`.

Then I had to remove a few unnecessary parens and muts that were exposed
now.

compiler/rustc_mir_dataflow/src/framework/direction.rs

@@ -196,7 +196,7 @@ impl Direction for Backward {
     {
         results.reset_to_block_entry(state, block);
 
-        vis.visit_block_end(results, &state, block_data, block);
+        vis.visit_block_end(results, state, block_data, block);
 
         // Terminator
         let loc = Location { block, statement_index: block_data.statements.len() };