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_codegen_ssa/src/debuginfo/type_names.rs

@@ -216,7 +216,7 @@ fn push_debuginfo_type_name<'tcx>(
                 output.push(']');
             }
         }
-        ty::Dynamic(ref trait_data, ..) => {
+        ty::Dynamic(trait_data, ..) => {
             let auto_traits: SmallVec<[DefId; 4]> = trait_data.auto_traits().collect();
 
             let has_enclosing_parens = if cpp_like_debuginfo {