Clean up some hints

pkg/analysis_server/test/services/correction/assist_test.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.
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/edit/assist/assist_dart.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
@@ skipping 494 matching lines @@
 import 'my_lib.dart';
 part 'test.dart';
 ''';
     testCode = r'''
 part of my_app;
 main() {
   var v = getFutureInt();
 }
 ''';
     // add sources
-    Source appSource = addSource('/app.dart', appCode);
+    addSource('/app.dart', appCode);
     testSource = addSource('/test.dart', testCode);
     // resolve
     await resolveTestUnit(testCode);
     // prepare the assist
     offset = findOffset('v = ');
     assist = await _assertHasAssist(DartAssistKind.ADD_TYPE_ANNOTATION);
     change = assist.change;
     // verify
     {
       var testFileEdit = change.getFileEdit('/app.dart');
@@ skipping 4230 matching lines @@
 
   @override
   final AstProvider astProvider;
 
   @override
   final CompilationUnit unit;
 
   _DartAssistContextForValues(this.source, this.selectionOffset,
       this.selectionLength, this.analysisDriver, this.astProvider, this.unit);
 }