Remove Expect from core library.

tests/language/gvn_interceptor_test.dart

Index: tests/language/gvn_interceptor_test.dart
diff --git a/tests/language/gvn_interceptor_test.dart b/tests/language/gvn_interceptor_test.dart
index 9e75f20f25acce73f379c1cb65aa2b0dd1de9ba4..d638a232ce6fc2c1ef9b21f7b34f46e50ca925c9 100644
--- a/tests/language/gvn_interceptor_test.dart
+++ b/tests/language/gvn_interceptor_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";
+
 foo(a, index) {
   if (a.length < index) {
    for (int i = a.length; i <= index; i++) a.add(i);