Get rid of more () in getter definitions.

tests/compiler/dart2js/dart_backend_test.dart

 // Copyright (c) 2012, 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:uri';
 import 'parser_helper.dart';
 import 'mock_compiler.dart';
 import '../../../lib/compiler/compiler.dart';
 import '../../../lib/compiler/implementation/dart2jslib.dart' as leg;
 import '../../../lib/compiler/implementation/dart_backend/dart_backend.dart';
@@ skipping 23 matching lines @@
 const ioLib = r'''
 #library('io');
 class Platform {
   static int operatingSystem;
 }
 ''';
 
 const htmlLib = r'''
 #library('html');
 Window __window;
-Window get window() => __window;
+Window get window => __window;
 abstract class Window {
-  abstract Navigator get navigator;
+  Navigator get navigator;
 }
 abstract class Navigator {
-  abstract String get userAgent;
+  String get userAgent;
 }
 ''';
 
 const helperLib = r'''
 #library('js_helper');
 ''';
 
 testDart2Dart(String src, {void continuation(String s), bool minify: false,
     bool stripTypes: false}) {
   // If continuation is not provided, check that source string remains the same.
@@ skipping 747 matching lines @@
   testInterfaceDefaultAnotherLib();
   testStaticAccessIoLib();
   testLocalFunctionPlaceholder();
   testMinification();
   testClosureLocalsMinified();
   testParametersMinified();
   testTypeVariablesInDifferentLibraries();
   testDeclarationTypePlaceholders();
   testPlatformLibraryMemberNamesAreFixed();
 }