Remove support for interface in dart2js.

sdk/lib/_internal/compiler/implementation/tree/prettyprint.dart

 // Copyright (c) 2012, 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.
 
 part of tree;
 
 /**
  * Pretty-prints Node tree in XML-like format.
  *
  * TODO(smok): Add main() to run from command-line to print out tree for given
@@ skipping 134 matching lines @@
   }
 
   visitClassNode(ClassNode node) {
     openNode(node, "ClassNode", {
       "extendsKeyword" : tokenToStringOrNull(node.extendsKeyword)
     });
     visitChildNode(node.name, "name");
     visitChildNode(node.superclass, "superclass");
     visitChildNode(node.interfaces, "interfaces");
     visitChildNode(node.typeParameters, "typeParameters");
-    visitChildNode(node.defaultClause, "defaultClause");
     closeNode();
   }
 
   visitConditional(Conditional node) {
     visitNodeWithChildren(node, "Conditional");
   }
 
   visitContinueStatement(ContinueStatement node) {
     visitNodeWithChildren(node, "ContinueStatement");
   }
@@ skipping 309 matching lines @@
   }
 
   visitStringNode(StringNode node) {
     unimplemented('visitNode', node: node);
   }
 
   unimplemented(String message, {Node node}) {
     throw message;
   }
 }