Migrate language/arithmetic2_test ... language/async_await_syntax_test.

tests/language/assert_trailing_comma_test.dart

Index: tests/language/assert_trailing_comma_test.dart
diff --git a/tests/language/assert_trailing_comma_test.dart b/tests/language/assert_trailing_comma_test.dart
deleted file mode 100644
index e0020312e186445ea8379d456ef0631cd8252b38..0000000000000000000000000000000000000000
--- a/tests/language/assert_trailing_comma_test.dart
+++ /dev/null
@@ -1,12 +0,0 @@
-// Copyright (c) 2017, 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.
-
-main() {
-  assert(true);
-  assert(true,);
-  assert(true,"message");
-  assert(true,"message",);
-  assert(true,"message",extra);  //# 01: compile-time error
-  assert(true,"message",,);  //# 02: compile-time error
-}