Remove Expect from core library.

tests/language/is_function_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";
+
 var staticClosure;
 staticMethod() => 42;
 
 class B {
   var instanceClosure;
   var nullField;
   instanceMethod() => 43;
 }
 
 checkUntyped(closure) {
@@ skipping 34 matching lines @@
 
   checkUntyped(closureStatement);
   checkTyped(closureStatement);
 
   checkUntyped(closureExpression);
   checkTyped(closureExpression);
 
   checkTypedNull(b.nullField);
   checkUntypedNull(b.nullField);
 }