Revert "Search for main in the exported names of the main library, not in the library itself."

tests/language/export_ambiguous_main_b.dart

Index: tests/language/export_ambiguous_main_b.dart
diff --git a/tests/language/export_ambiguous_main_b.dart b/tests/language/export_ambiguous_main_b.dart
deleted file mode 100644
index 734a620649cd97b363dfd90b43161afc6d14b07e..0000000000000000000000000000000000000000
--- a/tests/language/export_ambiguous_main_b.dart
+++ /dev/null
@@ -1,9 +0,0 @@
-// Copyright (c) 2013, 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 export_ambiguous_main_b;
-
-main() {
-  print('export_ambiguous_main_b');
-}