Remove Expect from core library.

tests/language/deoptimized_function_on_stack_test.dart

 // Copyright (c) 2011, 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.
 
+import "package:expect/expect.dart";
+
 // This is a test for deoptimization infrastructure and to reproduce the
 // failure from bug 5442338.
 
 main() {
   warmup();
   runTest();
 }
 
 // Create a situation where method 'call' is optimized for using class A
 // when calling foo. 
@@ skipping 32 matching lines @@
 
 
 class A {
   foo() { return 1; }
 }
 
 
 class B {
   foo() { return 2; }
 }