Fix analyzer hints and warnings in test/.

test/global/binstubs/binstub_runs_executable_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 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_process.dart';
-import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 import 'utils.dart';
 
 main() {
   integration("the generated binstub runs a snapshotted executable", () {
     servePackages((builder) {
       builder.serve("foo", "1.0.0", pubspec: {
         "executables": {
@@ skipping 34 matching lines @@
 
     var process = new ScheduledProcess.start(
         p.join(sandboxDir, cachePath, "bin", binStubName("foo-script")),
         ["arg1", "arg2"],
         environment: getEnvironment());
 
     process.stdout.expect("ok [arg1, arg2]");
     process.shouldExit();
   });
 }