[dart:io] Remove DART_IO_DISABLED

runtime/bin/sync_socket_fuchsia.cc

Index: runtime/bin/sync_socket_fuchsia.cc
diff --git a/runtime/bin/sync_socket_fuchsia.cc b/runtime/bin/sync_socket_fuchsia.cc
index 8148b8a7e6f4de8dbfd9556dc150d9b25aa09cbf..3a6fe0d254054601d18e0e6ecb7309b3799e43b7 100644
--- a/runtime/bin/sync_socket_fuchsia.cc
+++ b/runtime/bin/sync_socket_fuchsia.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 "platform/globals.h"
 #if defined(HOST_OS_FUCHSIA)
 
@@ -92,5 +90,3 @@ void SynchronousSocket::Close(intptr_t fd) {
 }  // namespace dart
 
 #endif  // defined(HOST_OS_FUCHSIA)
-
-#endif  // !defined(DART_IO_DISABLED)