Remove Expect from core library.

tests/lib/crypto/hmac_sha256_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.
 
 // Library tag to allow the test to run on Dartium.
 library hmac_sha256_test;
 
+import "package:expect/expect.dart";
 import 'dart:crypto';
 
 part 'hmac_sha256_test_vectors.dart';
 
 void testStandardVectors(inputs, keys, macs) {
   for (var i = 0; i < inputs.length; i++) {
     var hmac = new HMAC(new SHA256(), keys[i]);
     hmac.add(inputs[i]);
     var d = hmac.close();
     Expect.isTrue(CryptoUtils.bytesToHex(d).startsWith(macs[i]), '$i');
   }
 }
 
 void main() {
   testStandardVectors(hmac_sha256_inputs, hmac_sha256_keys, hmac_sha256_macs);
 }