Clean up hints after a new hint was introduced

pkg/analyzer/lib/src/generated/constant.dart

 // Copyright (c) 2014, 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 analyzer.src.generated.constant;
 
 import 'package:analyzer/context/declared_variables.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/constant/evaluation.dart';
 import 'package:analyzer/src/dart/constant/value.dart';
 import 'package:analyzer/src/generated/engine.dart';
-import 'package:analyzer/src/generated/engine.dart'
-    show AnalysisEngine, RecordingErrorListener;
+import 'package:analyzer/src/generated/engine.dart' show RecordingErrorListener;
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/resolver.dart' show TypeProvider;
 import 'package:analyzer/src/generated/source.dart' show Source;
 import 'package:analyzer/src/generated/type_system.dart'
     show TypeSystem, TypeSystemImpl;
 
 export 'package:analyzer/context/declared_variables.dart';
 export 'package:analyzer/dart/constant/value.dart';
 export 'package:analyzer/src/dart/constant/evaluation.dart';
 export 'package:analyzer/src/dart/constant/utilities.dart';
@@ skipping 105 matching lines @@
     DartObjectImpl result = expression.accept(new ConstantVisitor(
         new ConstantEvaluationEngine(_typeProvider, new DeclaredVariables(),
             typeSystem: _typeSystem),
         errorReporter));
     if (result != null) {
       return EvaluationResult.forValue(result);
     }
     return EvaluationResult.forErrors(errorListener.errors);
   }
 }