Revert "Add typedef AST node boilerplate."

pkg/kernel/lib/transformations/reify/transformation/remove_generics.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library kernel.transformations.reify.transformation.remove_generics;
 
 import 'package:kernel/ast.dart';
 import 'transformer.dart';
 
 class Erasure extends Transformer with DartTypeVisitor<DartType> {
@@ skipping 42 matching lines @@
 
   @override
   InterfaceType visitInterfaceType(InterfaceType type) {
     if (removeTypeParameters(type.classNode)) {
       return new InterfaceType(type.classNode, const <DartType>[]);
     }
     return type;
   }
 
   @override
-  TypedefType visitTypedefType(TypedefType type) {
-    throw 'Typedef types not implemented in erasure';
-  }
-
-  @override
   Supertype visitSupertype(Supertype type) {
     if (removeTypeParameters(type.classNode)) {
       return new Supertype(type.classNode, const <DartType>[]);
     }
     return type;
   }
 
   @override
   FunctionType visitFunctionType(FunctionType type) {
     bool partHasChanged = false;
@@ skipping 56 matching lines @@
     }
     return node;
   }
 
   @override
   Expression visitMethodInvocation(MethodInvocation node) {
     node.transformChildren(this);
     return removeTypeArgumentOfMethodInvocation(node);
   }
 }