Revert "Added synchronous socket implementation to dart:io."

runtime/bin/io_impl_sources.gypi

 # Copyright (c) 2012, 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.
 
 # This file contains some C++ sources for the dart:io library.  The other
 # implementation files are in builtin_impl_sources.gypi.
 {
   'sources': [
     'eventhandler.cc',
     'eventhandler.h',
@@ skipping 72 matching lines @@
     'socket_unsupported.cc',
     'socket_win.cc',
     'stdio.cc',
     'stdio.h',
     'stdio_android.cc',
     'stdio_fuchsia.cc',
     'stdio_linux.cc',
     'stdio_macos.cc',
     'stdio_unsupported.cc',
     'stdio_win.cc',
-    'sync_socket.cc',
-    'sync_socket.h',
-    'sync_socket_android.cc',
-    'sync_socket_fuchsia.cc',
-    'sync_socket_linux.cc',
-    'sync_socket_macos.cc',
-    'sync_socket_win.cc',
   ],
 }