Fix analyzer hints and warnings in test/.

test/transformer/configuration/configuration_defaults_to_empty_map_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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:convert';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
@@ skipping 34 matching lines @@
        }),
        d.dir("lib", [d.dir("src", [
          d.file("transformer.dart", transformer)
        ])]),
        d.dir("web", [
          d.file("foo.txt", "foo")
        ])
      ]).create();
 
      pubGet();
-     var server = pubServe();
+     pubServe();
      requestShouldSucceed("foo.json", JSON.encode({}));
      endPubServe();
    });
 }