Revert "Report errors on duplicate export."

tests/language/duplicate_export_negative_test.dart

Index: tests/language/duplicate_export_negative_test.dart
diff --git a/tests/language/duplicate_export_negative_test.dart b/tests/language/duplicate_export_negative_test.dart
deleted file mode 100644
index 51a2294d7f9bdbc137ca8eb0d76209577db1aaa5..0000000000000000000000000000000000000000
--- a/tests/language/duplicate_export_negative_test.dart
+++ /dev/null
@@ -1,8 +0,0 @@
-// Copyright (c) 2012, 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 'duplicate_import_libd.dart';
-
-void main() {
-}