Fix analyzer hints and warnings in test/.

test/validator/sdk_constraint_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:async';
-import 'dart:convert';
-
-import 'package:http/http.dart' as http;
-import 'package:http/testing.dart';
-import 'package:path/path.dart' as path;
 import 'package:pub/src/entrypoint.dart';
 import 'package:pub/src/validator.dart';
 import 'package:pub/src/validator/sdk_constraint.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 import 'utils.dart';
 
 Validator sdkConstraint(Entrypoint entrypoint) =>
@@ skipping 16 matching lines @@
 
   test("should consider a package invalid if it has an SDK constraint with "
       "^", () {
     d.dir(appPath, [
       d.libPubspec("test_pkg", "1.0.0", sdk: "^1.8.0")
     ]).create();
     expect(schedulePackageValidation(sdkConstraint),
         completion(pairOf(anyElement(contains('">=1.8.0 <2.0.0"')), isEmpty)));
   });
 }