dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/universe/world_impact.dart

 // Copyright (c) 2015, 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.universe.world_impact;
 
-import '../elements/elements.dart'
-    show Element, LocalFunctionElement, MethodElement;
+import '../elements/elements.dart' show Element;
 import '../util/util.dart' show Setlet;
-
 import 'use.dart' show DynamicUse, StaticUse, TypeUse;
 
 class WorldImpact {
   const WorldImpact();
 
   Iterable<DynamicUse> get dynamicUses => const <DynamicUse>[];
 
   Iterable<StaticUse> get staticUses => const <StaticUse>[];
 
   // TODO(johnniwinther): Replace this by called constructors with type
@@ skipping 203 matching lines @@
     }
   }
 
   @override
   void visitTypeUse(TypeUse use) {
     if (_visitTypeUse != null) {
       _visitTypeUse(use);
     }
   }
 }