Revert "Report errors on duplicate export."

tests/language/duplicate_import_liba.dart

Index: tests/language/duplicate_import_liba.dart
diff --git a/tests/language/duplicate_import_liba.dart b/tests/language/duplicate_import_liba.dart
deleted file mode 100644
index b8af1a7da6842538fc68e1582dd8a51a45acfce2..0000000000000000000000000000000000000000
--- a/tests/language/duplicate_import_liba.dart
+++ /dev/null
@@ -1,13 +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.
-
-library liba;
-
-var field;
-
-void method() {}
-
-class Class {}
-
-void methodOrClass() {}