Remove custom expect.dart from Kernel tests

tests/kernel/unsorted/symbol_literal_test.dart

Index: tests/kernel/unsorted/symbol_literal_test.dart
diff --git a/tests/kernel/unsorted/symbol_literal_test.dart b/tests/kernel/unsorted/symbol_literal_test.dart
index 53af588fde53defb7cf6ecb14c2762949b08d31e..6a3cc8a1d97e2fe7a78fbf48403bf0a62f42b09f 100644
--- a/tests/kernel/unsorted/symbol_literal_test.dart
+++ b/tests/kernel/unsorted/symbol_literal_test.dart
@@ -2,7 +2,7 @@
 // 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';
 
 main() {
   Expect.isTrue('${#abc}' == 'Symbol("abc")');