Remove is_empty check in filter_assoc_items_by_name_and_namespace.

It was added in #140052, but the subsequent changes in #140252 means it
is no longer necessary. (Indeed, `Ident`s cannot be empty any more.)

Author: nnethercote

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -59,12 +59,7 @@ fn filter_assoc_items_by_name_and_namespace(
 ident:Ident,
 ns:Namespace,
 ) -> implIterator<Item = &ty::AssocItem>{
-let iter:Box<dynIterator<Item = &ty::AssocItem>> = if !ident.name.is_empty(){
-Box::new(tcx.associated_items(assoc_items_of).filter_by_name_unhygienic(ident.name))
-}else{
-Box::new([].iter())
-};
- iter.filter(move |item| {
+ tcx.associated_items(assoc_items_of).filter_by_name_unhygienic(ident.name).filter(move |item| {
  item.namespace() == ns && tcx.hygienic_eq(ident, item.ident(tcx), assoc_items_of)
 })
 }