[dart:io] Remove DART_IO_DISABLED

runtime/bin/directory.cc

Index: runtime/bin/directory.cc
diff --git a/runtime/bin/directory.cc b/runtime/bin/directory.cc
index 18d2629f5dc8f24e83f1c5ef18f918bd475ed2f0..e31779c950da2766434e145e344e8ad120ac68ad 100644
--- a/runtime/bin/directory.cc
+++ b/runtime/bin/directory.cc
@@ -2,8 +2,6 @@
 // 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.
 
-#if !defined(DART_IO_DISABLED)
-
 #include "bin/directory.h"
 
 #include "bin/dartutils.h"
@@ -467,5 +465,3 @@ void Directory::List(DirectoryListing* listing) {
 
 }  // namespace bin
 }  // namespace dart
-
-#endif  // !defined(DART_IO_DISABLED)