Fix analyzer hints and warnings in test/.

test/global/run/implicit_executable_name_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 'package:pub/src/exit_codes.dart' as exit_codes;
-
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   integration('defaults to the package name if the script is omitted', () {
     servePackages((builder) {
       builder.serve("foo", "1.0.0", contents: [
         d.dir("bin", [
           d.file("foo.dart", "main(args) => print('foo');")
         ])
       ]);
     });
 
     schedulePub(args: ["global", "activate", "foo"]);
 
     var pub = pubRun(global: true, args: ["foo"]);
     pub.stdout.expect("foo");
     pub.shouldExit();
   });
 }