dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/serialization/serialization_util.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 dart2js.serialization.util;
 
+import '../constants/expressions.dart';
 import '../dart_types.dart';
-import '../common/resolution.dart';
-import '../constants/expressions.dart';
 import '../elements/elements.dart';
 import '../resolution/access_semantics.dart';
 import '../resolution/operators.dart';
 import '../resolution/send_structure.dart';
 import '../universe/call_structure.dart';
 import '../universe/selector.dart';
-import '../universe/world_impact.dart';
-import '../universe/use.dart';
-import '../util/enumset.dart';
-
 import 'keys.dart';
 import 'serialization.dart';
 
 /// Serialize [name] into [encoder].
 void serializeName(Name name, ObjectEncoder encoder) {
   encoder.setString(Key.NAME, name.text);
   encoder.setBool(Key.IS_SETTER, name.isSetter);
   if (name.library != null) {
     encoder.setElement(Key.LIBRARY, name.library);
   }
@@ skipping 442 matching lines @@
     case AccessKind.COMPOUND:
       CompoundAccessKind compoundAccessKind =
           decoder.getEnum(Key.SUB_KIND, CompoundAccessKind.values);
       Element getter = decoder.getElement(Key.GETTER);
       Element setter = decoder.getElement(Key.SETTER);
       return new CompoundAccessSemantics(compoundAccessKind, getter, setter);
     case AccessKind.CONSTANT:
       throw new UnsupportedError('Unsupported access kind: $kind');
   }
 }