Remove Expect from core library.

tests/language/lazy_map_test.dart

Index: tests/language/lazy_map_test.dart
diff --git a/tests/language/lazy_map_test.dart b/tests/language/lazy_map_test.dart
index f1ff770a22ef40b51d951b82d5abd979d7054b4b..65fb19b42cefa530c789a0c783b7e168b45c831f 100644
--- a/tests/language/lazy_map_test.dart
+++ b/tests/language/lazy_map_test.dart
@@ -2,6 +2,8 @@
 // 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:expect/expect.dart";
+
 var data = { 'a': 'a' };
 main() {
   Expect.equals('a', data['a']);