use Identifier instead of just a plain string when getting tuple-element-names

javascript/ql/src/semmlecode.javascript.dbscheme

@@ -790,13 +790,6 @@ tuple_type_rest(
   unique int typ: @type ref
 );
 
-#keyset[tuple, index]
-tuple_element_name (
-  int tuple: @tupletypeexpr ref,
-  int index: int ref,
-  varchar(900) name: string ref
-);
-
 // comments
 comments (unique int id: @comment,
           int kind: int ref,