Remove support for SDK dependencies.

utils/tests/pub/install/sdk/check_out_test.dart

-// Copyright (c) 2012, 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.
-
-library pub_tests;
-
-import 'dart:io';
-
-import '../../test_pub.dart';
-
-main() {
-  integration('checks out a package from the SDK', () {
-    dir(sdkPath, [
-      dir('pkg', [
-        dir('foo', [
-          libDir('foo', 'foo 0.1.2+3'),
-          libPubspec('foo', '0.0.0-not.used')
-        ])
-      ])
-    ]).scheduleCreate();
-
-    dir(appPath, [
-      pubspec({"name": "myapp", "dependencies": {"foo": {"sdk": "foo"}}})
-    ]).scheduleCreate();
-
-    schedulePub(args: ['install'],
-        output: new RegExp(r"Dependencies installed!$"));
-
-    packagesDir({"foo": "0.1.2+3"}).scheduleValidate();
-  });
-}