Enable issue tests that appear to be incorrectly named.

tests/language/isssue_21159.dart

Index: tests/language/isssue_21159.dart
diff --git a/tests/language/isssue_21159.dart b/tests/language/isssue_21159.dart
deleted file mode 100644
index 2d2b6c858ce7d8ed32049886a6179abe922f82b3..0000000000000000000000000000000000000000
--- a/tests/language/isssue_21159.dart
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright (c) 2014, 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.
-
-class C {
- get call => this;
-}
-
-main() {
- new C()();
-}