Avoid some unnecessary symbol interning.

- `Ident::from_str_and_span` -> `Ident::new` when the string is
  pre-interned.
- `Ident::from_str` -> `Ident::with_dummy_span` when the string is
  pre-interned.
- `_d` and `_e` are unused.

Author: nnethercote

clippy_lints/src/bool_assert_comparison.rs

@@ -56,7 +56,7 @@ fn is_impl_not_trait_with_bool_out<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -
         .and_then(|trait_id| {
             cx.tcx.associated_items(trait_id).find_by_ident_and_kind(
                 cx.tcx,
-                Ident::from_str("Output"),
+                Ident::with_dummy_span(sym::Output),
                 ty::AssocTag::Type,
                 trait_id,
             )