Replace no_ord_impl with orderable.

Similar to the previous commit, this replaces `newtype_index`'s opt-out
`no_ord_impl` attribute with the opt-in `orderable` attribute.

compiler/rustc_hir/src/hir_id.rs

@@ -155,6 +155,7 @@ rustc_index::newtype_index! {
     /// tree or hash map.
     #[derive(HashStable_Generic)]
     #[encodable]
+    #[orderable]
     pub struct ItemLocalId {}
 }