Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/throw_try_catch_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.
 
-import 'expect.dart';
+import 'package:expect/expect.dart';
 
 testSimpleThrowCatch() {
   var x = 1;
   try {
     throw x++;
   } on int catch (e) {
     Expect.isTrue(e == 1);
     Expect.isTrue(x == 2);
     x++;
   }
@@ skipping 165 matching lines @@
   testSiblingThrowCatch();
   testTypedCatch();
   testTypedCatch2();
   testThrowNull();
   testFinally();
   testFinally2();
   testFinally3();
   testSuccessfulBody();
   testSuccessfulBody2();
 }