Cleanup some unused code in some of the tests

pkg/analysis_server/test/services/dependencies/library_dependencies_test.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.
 
 import 'package:analysis_server/src/services/dependencies/library_dependencies.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../../abstract_context.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(LibraryDependenciesTest);
   });
 }
 
 @reflectiveTest
 class LibraryDependenciesTest extends AbstractContextTest {
   @failingTest
   test_LibraryDependencies() {
     // See https://github.com/dart-lang/sdk/issues/29310
     addSource('/lib1.dart', 'import "lib2.dart";');
     addSource('/lib2.dart', 'import "lib1.dart";');
     addSource('/lib3.dart', 'import "lib2.dart";');
     addSource('/lib4.dart', 'import "lib5.dart";');
     provider.newFile('/lib5.dart', 'import "lib6.dart";');
     provider.newFile('/lib6.dart', '');
 
-    _performAnalysis();
-
-    var libs =
-        new LibraryDependencyCollector([context]).collectLibraryDependencies();
+    var libs = new LibraryDependencyCollector([]).collectLibraryDependencies();
 
     // Cycles
     expect(libs, contains('/lib1.dart'));
     expect(libs, contains('/lib2.dart'));
     // Regular sources
     expect(libs, contains('/lib3.dart'));
     expect(libs, contains('/lib4.dart'));
     // Non-source, referenced by source
     expect(libs, contains('/lib5.dart'));
     // Non-source, referenced by non-source
     expect(libs, contains('/lib6.dart'));
   }
 
   test_PackageMaps() {
     //TODO(pquitslund): add test
   }
-
-  void _performAnalysis() {
-    while (context.performAnalysisTask().hasMoreWork) {}
-  }
 }