Fix analyzer hints and warnings in test/.

test/global/activate/outdated_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.
 
-import 'dart:io';
-import 'dart:async';
-
-import 'package:path/path.dart' as p;
-import 'package:scheduled_test/scheduled_process.dart';
-import 'package:scheduled_test/scheduled_stream.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 const _OUTDATED_BINSTUB = """
 #!/usr/bin/env sh
 # This file was created by pub v0.1.2-3.
 # Package: foo
 # Version: 1.0.0
@@ skipping 27 matching lines @@
     schedulePub(args: ["global", "activate", "foo"]);
 
     d.dir(cachePath, [
       d.dir('bin', [
         // 253 is the VM's exit code upon seeing an out-of-date snapshot.
         d.matcherFile(binStubName('foo-script'), contains("253"))
       ])
     ]).validate();
   });
 }