dart2js cleanup: remove unused imports and variables

pkg/compiler/lib/src/resolution/constructors.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.resolution.constructors;
 
 import '../common.dart';
 import '../common/resolution.dart' show Feature;
 import '../compiler.dart' show Compiler;
 import '../constants/constructors.dart'
@@ skipping 153 matching lines @@
 
     bool isSuperCall = Initializers.isSuperConstructorCall(node);
     InterfaceType targetType =
         getSuperOrThisLookupTarget(node, isSuperCall: isSuperCall);
     ClassElement lookupTarget = targetType.element;
     String constructorName =
         visitor.getRedirectingThisOrSuperConstructorName(node).text;
     ConstructorElement foundConstructor =
         findConstructor(constructor.library, lookupTarget, constructorName);
 
-    final bool isImplicitSuperCall = false;
     final String className = lookupTarget.name;
     CallStructure callStructure = argumentsResult.callStructure;
     ConstructorElement calledConstructor = verifyThatConstructorMatchesCall(
         node, foundConstructor, callStructure, className,
         constructorName: constructorName,
         isThisCall: !isSuperCall,
         isImplicitSuperCall: false);
     // TODO(johnniwinther): Remove this when information is pulled from an
     // [InitializerStructure].
     registry.useElement(node, calledConstructor);
@@ skipping 665 matching lines @@
     // constructors.
     return null;
   }
   // TODO(johnniwinther): Use [Name] for lookup.
   ConstructorElement constructor = cls.lookupConstructor(constructorName);
   if (constructor != null) {
     constructor = constructor.declaration;
   }
   return constructor;
 }