Remove Expect from core library.

tests/language/math_vm_test.dart

 // Copyright (c) 2012, 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.
 // Tests that the VM does not crash on weird corner cases of class Math.
 // VMOptions=--optimization_counter_threshold=100
 
 library math_vm_test;
 
+import "package:expect/expect.dart";
 import 'dart:math';
 
 class FakeNumber {
   const FakeNumber();
   void toDouble() {}
 }
 
 class MathTest {
   static bool testParseInt(x) {
     try {
@@ skipping 23 matching lines @@
   Expect.equals((1 << 32).toDouble(), pow(2.0, 32));
 }
 
 
 main() {
   for (int i = 0; i < 200; i++) {
     MathTest.testMain();
     testDoublePow();
   }
 }