Remove Expect from core library.

tests/standalone/io/options_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.
 // Stress test isolate generation.
 // DartOptions=tests/standalone/io/options_test.dart 10 options_test 20
 
+import "package:expect/expect.dart";
 import "dart:math";
 import "dart:io";
 
 main() {
   var opts = new Options();
 
   // Basic test for functionality.
   Expect.equals(3, opts.arguments.length);
   Expect.equals(10, int.parse(opts.arguments[0]));
   Expect.equals("options_test", opts.arguments[1]);
@@ skipping 10 matching lines @@
   Expect.equals(20, int.parse(opts.arguments[2]));
   Expect.equals("Fourth", opts.arguments[3]);
 
   // Check that a new options object still gets the original arguments.
   var opts2 = new Options();
   Expect.equals(3, opts2.arguments.length);
   Expect.equals(10, int.parse(opts2.arguments[0]));
   Expect.equals("options_test", opts2.arguments[1]);
   Expect.equals(20, int.parse(opts2.arguments[2]));
 }