Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/block_scope_test.dart

 // Copyright (c) 2016, 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.
 
 // Tests of block scoping.
 
-import 'expect.dart';
+import 'package:expect/expect.dart';
 
 bool oracle() => true;
 
 test0() {
   var x = 'outer', y = x;
   Expect.isTrue(x == 'outer');
   Expect.isTrue(y == 'outer');
   { var x = 'inner';
     Expect.isTrue(x == 'inner');
     Expect.isTrue(y == 'outer');
@@ skipping 32 matching lines @@
   } else {
     Expect.isTrue(false);
   }
   Expect.isTrue(x == 'toplevel');
   Expect.isTrue(y == 'outer');
 }
 
 main() {
   test0();
   test1();
-}  
+}