Fix some unwanted uses of Debug formatting on user-facing messages

While formatting for user diagnostics used `Display` for all most cases,
some small amount of cases used `Debug` instead.  Until now, `Display`
and `Debug` yielded the same output for many types. However, with path
trimming, we want to show a shorter path for the user, these cases need
fixing.

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1342,8 +1342,8 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
                     .normalize(candidate)
                     .ok();
                 match normalized {
-                    Some(normalized) => format!("\n  {:?}", normalized.value),
-                    None => format!("\n  {:?}", candidate),
+                    Some(normalized) => format!("\n  {}", normalized.value),
+                    None => format!("\n  {}", candidate),
                 }
             })
         };