Remove Expect from core library.

tests/language/method_invocation_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";
+
 // Testing method invocation.
 // Currently testing only NoSuchMethodError.
 
 class A {
   A() {}
   int foo() {
     return 1;
   }
 }
 
@@ skipping 12 matching lines @@
   }
 
   static void testMain() {
     testNullReceiver();
   }
 }
 
 main() {
   MethodInvocationTest.testMain();
 }