Remove is_empty check in filter_assoc_items_by_name_and_namespace.

It was added in rust-lang#140052, but the subsequent changes in rust-lang#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,
 ) -> impl Iterator<Item = &ty::AssocItem> {
-    let iter: Box<dyn Iterator<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)
     })
 }