Remove Expect from core library.

tests/language/compile_time_constant_a_test.dart

Index: tests/language/compile_time_constant_a_test.dart
diff --git a/tests/language/compile_time_constant_a_test.dart b/tests/language/compile_time_constant_a_test.dart
index 73ff7de6ab522332ab6d5e68ac2f6c119a5b4d12..576939f0aec8b4279c1ebcc71400dc93af7a5142 100644
--- a/tests/language/compile_time_constant_a_test.dart
+++ b/tests/language/compile_time_constant_a_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";
+
 const m1 = const { 'a': 400 + 99 };
 const m2 = const { 'a': 499, 'b': 42 };
 const m3 = const { 'm1': m1, 'm2': m2 };