Fix analyzer hints and warnings in test/.

test/global/run/errors_if_outside_bin_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:path/path.dart' as p;
 import 'package:pub/src/exit_codes.dart' as exit_codes;
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
 
 main() {
   integration('errors if the script is in a subdirectory.', () {
     servePackages((builder) {
       builder.serve("foo", "1.0.0", contents: [
         d.dir("example", [
@@ skipping 11 matching lines @@
 -h, --help            Print this usage information.
 -c, --[no-]checked    Enable runtime type checks and assertions.
     --mode            Mode to run transformers in.
                       (defaults to "release")
 
 Run "pub help" to see global options.
 """,
         exitCode: exit_codes.USAGE);
   });
 }