Remove Expect from core library.

tests/language/compile_time_constant_b_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";
+
 const m1 = const { '__proto__': 400 + 99 };
 const m2 = const { 'a': 499, 'b': 42 };
 const m3 = const { '__proto__': 499 };
 
 bool isUnsupportedError(o) => o is UnsupportedError;
 
 main() {
   Expect.equals(499, m1['__proto__']);
   Expect.equals(null, m1['b']);
   Expect.listEquals(['__proto__'], m1.keys.toList());
@@ skipping 51 matching lines @@
   Expect.throws(() => m2['a'] = 499, isUnsupportedError);
   Expect.throws(() => m2['b'] = 42, isUnsupportedError);
   Expect.throws(() => m2['__proto__'] = 499, isUnsupportedError);
   Expect.throws(() => m2.putIfAbsent('a', () => 499), isUnsupportedError);
   Expect.throws(() => m2.putIfAbsent('__proto__', () => 499),
                 isUnsupportedError);
   Expect.throws(() => m2['a'] = 499, isUnsupportedError);
 
   Expect.isTrue(m1 === m3);
 }