Remove Expect from core library.

tests/language/compile_time_constant_k_test.dart

Index: tests/language/compile_time_constant_k_test.dart
diff --git a/tests/language/compile_time_constant_k_test.dart b/tests/language/compile_time_constant_k_test.dart
index 2071587491974e4ed92713ff2e3349545c658235..f4260a3e5b9ffbaeb32b3393c9120280fc4e83c8 100644
--- a/tests/language/compile_time_constant_k_test.dart
+++ b/tests/language/compile_time_constant_k_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 x = const { 'a': 3, 'a': 4 };
 const y = const { 'a': 10, 'b': 11, 'a': 12, 'b': 13, 'a': 14 };
 const z = const { '__proto__': 496,