Revert "Ensure that failure to start an isolate all end up in the future."

tests/isolate/isolate_create_error_helper_lib5.dart

Index: tests/isolate/isolate_create_error_helper_lib5.dart
diff --git a/tests/isolate/isolate_create_error_helper_lib5.dart b/tests/isolate/isolate_create_error_helper_lib5.dart
deleted file mode 100644
index 505ffa1036382c675850c95b02f2c924408d3576..0000000000000000000000000000000000000000
--- a/tests/isolate/isolate_create_error_helper_lib5.dart
+++ /dev/null
@@ -1,13 +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.
-
-library isolate.create.error_helper5_lib;
-
-// This library has a main that is not a function,
-// but is a constant with a function type.
-
-
-void mymain() { print("Not call mymain function!"); }
-
-const main = mymain;