Remove deprecated Expect from the libraries.

tests/language/mixin_lib_extends_field_test.dart

 // Copyright (c) 2013, 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 mixin_lib_extends_field_test;
 
+import 'package:expect/expect.dart';
 import "mixin_lib_extends_field_lib.dart" as L;
 
 class S {
   var foo = "S-foo";
 }
 
 class C extends S with L.M1 { }
 class D extends S with L.M1, L.M2 { }
 class E extends S with L.M2, L.M1 { }
 
@@ skipping 88 matching lines @@
   Expect.throws(() => c.fez = 0, (error) => error is NoSuchMethodError);
   Expect.throws(() => d.fez = 0, (error) => error is NoSuchMethodError);
   Expect.throws(() => e.fez = 0, (error) => error is NoSuchMethodError);
 
   f.fez = "F-fez-f";
   Expect.throws(() => c.fez, (error) => error is NoSuchMethodError);
   Expect.throws(() => d.fez, (error) => error is NoSuchMethodError);
   Expect.throws(() => e.fez, (error) => error is NoSuchMethodError);
   Expect.equals("F-fez-f", f.fez);
 }