Fix analyzer hints and warnings in test/.

test/cache/repair/handles_corrupted_binstub_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.
 
 library pub_tests;
 
-import 'dart:io';
-
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   integration('handles a corrupted binstub script', () {
     servePackages((builder) {
       builder.serve("foo", "1.0.0", contents: [
         d.dir("bin", [
           d.file("script.dart", "main(args) => print('ok');")
         ])
       ]);
     });
 
     schedulePub(args: ["global", "activate", "foo"]);
 
     d.dir(cachePath, [
       d.dir('bin', [
         d.file(binStubName('script'), 'junk')
       ])
     ]).create();
 
     schedulePub(args: ["cache", "repair"],
         error: contains('Error reading binstub for "script":'));
   });
 }