Remove Expect from core library.

tests/language/abstract_runtime_error_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.
 
+import "package:expect/expect.dart";
+
 // Test various conditions around instantiating an abstract class.
 
 // From The Dart Programming Langauge Specification, 11.11.1 "New":
 //   If q is a constructor of an abstract class then an
 //   AbstractClassInstantiation- Error is thrown.
 
 
 abstract class Interface {
   void foo();
 }
@@ skipping 19 matching lines @@
 }
 
 void main() {
   Expect.throws(interface, isAbstractClassInstantiationError,
                 "expected AbstractClassInstantiationError");
   Expect.throws(abstractClass, isAbstractClassInstantiationError,
                 "expected AbstractClassInstantiationError");
   Expect.stringEquals('ConcreteSubclass', '${new ConcreteSubclass()}');
   Expect.stringEquals('NonAbstractClass', '${new NonAbstractClass()}');
 }