Fix obsolete ref

Author: eernstg

specification/dartLangSpec.tex

@@ -22350,7 +22350,7 @@ \subsection{Static Types}
   A \synt{typeIdentifier} is an identifier which can be the name of a type,
   that is,
   it denotes an \synt{IDENTIFIER} which is not a \synt{BUILT\_IN\_IDENTIFIER}
-  (\ref{identifierReference}).%
+  (\ref{identifierExpression}).%
 }
 
 \commentary{%
@@ -26882,7 +26882,7 @@ \subsubsection{Reserved Words}
 \LMHash{}%
 In the grammar, the rule for reserved words above must occur
 before the rule for \synt{BUILT\_IN\_IDENTIFIER}
-(\ref{identifierReference}).
+(\ref{identifierExpression}).
 
 \commentary{%
   This ensures that \synt{IDENTIFIER} and \synt{IDENTIFIER\_NO\_DOLLAR} do not