Clean up some hints

pkg/analysis_server/test/services/refactoring/rename_library_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 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'abstract_rename.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(RenameLibraryTest);
   });
@@ skipping 18 matching lines @@
         expectedMessage: "Library name must not be blank.");
     // same name
     refactoring.newName = 'my.app';
     assertRefactoringStatus(
         refactoring.checkNewName(), RefactoringProblemSeverity.FATAL,
         expectedMessage:
             "The new name must be different than the current name.");
   }
 
   test_createChange() async {
-    Source unitSource = addSource(
+    addSource(
         '/part.dart',
         '''
 part of my.app;
 ''');
     await indexTestUnit('''
 library my.app;
 part 'part.dart';
 ''');
     // configure refactoring
     _createRenameRefactoring();
     expect(refactoring.refactoringName, 'Rename Library');
     expect(refactoring.elementKindName, 'library');
     refactoring.newName = 'the.new.name';
     // validate change
     await assertSuccessfulRefactoring('''
 library the.new.name;
 part 'part.dart';
 ''');
     assertFileChangeResult(
         '/part.dart',
         '''
 part of the.new.name;
 ''');
   }
 
   test_createChange_hasWhitespaces() async {
-    Source unitSource = addSource(
+    addSource(
         '/part.dart',
         '''
 part of my .  app;
 ''');
     await indexTestUnit('''
 library my    . app;
 part 'part.dart';
 ''');
     // configure refactoring
     _createRenameRefactoring();
     expect(refactoring.refactoringName, 'Rename Library');
     expect(refactoring.elementKindName, 'library');
     refactoring.newName = 'the.new.name';
     // validate change
     await assertSuccessfulRefactoring('''
 library the.new.name;
 part 'part.dart';
 ''');
     assertFileChangeResult(
         '/part.dart',
         '''
 part of the.new.name;
 ''');
   }
 
   void _createRenameRefactoring() {
     createRenameRefactoringForElement(testUnitElement.library);
   }
 }