Remove Expect from core library.

tests/language/incr_op_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.
 // Dart test program for testing increment operator.
 
+import "package:expect/expect.dart";
+
 class A {
   static var yy;
   static set y(v) {
     yy = v;
   }
 
   static get y {
     return yy;
   }
 }
@@ skipping 58 matching lines @@
     Expect.equals(1 + 2, list[1]);
     Expect.equals(1 + 2, list[1]--);
     Expect.equals(1 + 1, list[1]);
     Expect.equals(1 + 0, --list[1]);
   }
 }
 
 main() {
   IncrOpTest.testMain();
 }