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

tests/language/export_ambiguous_main_negative_test.dart

Index: tests/language/export_ambiguous_main_negative_test.dart
diff --git a/tests/language/export_ambiguous_main_negative_test.dart b/tests/language/export_ambiguous_main_negative_test.dart
deleted file mode 100644
index 6087c676ce56467fa333094d58c77e909128b5e7..0000000000000000000000000000000000000000
--- a/tests/language/export_ambiguous_main_negative_test.dart
+++ /dev/null
@@ -1,6 +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.
-
-export 'export_ambiguous_main_a.dart';
-export 'export_ambiguous_main_b.dart';