dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

 // Copyright (c) 2013, 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 dart2js.ir_nodes;
 
 import 'dart:collection';
 import 'cps_fragment.dart' show CpsFragment;
 import 'cps_ir_nodes_sexpr.dart';
 import '../constants/values.dart' as values;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
@@ skipping 2080 matching lines @@
     conditionRef.parent = this;
     trueContinuationRef.parent = this;
     falseContinuationRef.parent = this;
   }
 }
 
 // ----------------------------------------------------------------------------
 //                            UTILITY STUFF
 // ----------------------------------------------------------------------------
 
-Reference<Primitive> _reference(Primitive definition) {
-  return new Reference<Primitive>(definition);
-}
-
 Reference<Primitive> _optionalReference(Primitive definition) {
   return definition == null ? null : new Reference<Primitive>(definition);
 }
 
 List<Reference<Primitive>> _referenceList(Iterable<Primitive> definitions) {
   return definitions.map((e) => new Reference<Primitive>(e)).toList();
 }
 
 Iterable<Primitive> _dereferenceList(List<Reference<Primitive>> references) {
   return references.map((ref) => ref.definition);
@@ skipping 1003 matching lines @@
         _definitions.getCopy(node.conditionRef),
         _copies[node.trueContinuation],
         _copies[node.falseContinuation],
         node.sourceInformation)..isStrictCheck = node.isStrictCheck);
   }
 
   visitUnreachable(Unreachable node) {
     plug(new Unreachable());
   }
 }