[dart:io] Remove DART_IO_DISABLED

runtime/bin/stdio.cc

Index: runtime/bin/stdio.cc
diff --git a/runtime/bin/stdio.cc b/runtime/bin/stdio.cc
index 2ebea1e587c5cf5a334a0d940ee1012b11361c71..5ba32ba89c1ab4ed7e1d44d3530c9a4b9cb2012f 100644
--- a/runtime/bin/stdio.cc
+++ b/runtime/bin/stdio.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/stdio.h"
 
 #include "bin/builtin.h"
@@ -117,5 +115,3 @@ void FUNCTION_NAME(Stdout_AnsiSupported)(Dart_NativeArguments args) {
 
 }  // namespace bin
 }  // namespace dart
-
-#endif  // !defined(DART_IO_DISABLED)