[dart:io] Move Platform.ansiSupported to {Stdin,Stdout}.supportsAnsiEscapes

runtime/bin/platform_linux.cc

 // 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.
 
 #include "platform/globals.h"
 #if defined(HOST_OS_LINUX)
 
 #include "bin/platform.h"
 
 #include <signal.h>  // NOLINT
@@ skipping 92 matching lines @@
   }
   return result;
 }
 
 
 const char* Platform::ResolveExecutablePath() {
   return File::LinkTarget("/proc/self/exe");
 }
 
 
-bool Platform::AnsiSupported() {
-  return true;
-}
-
-
 void Platform::Exit(int exit_code) {
   exit(exit_code);
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(HOST_OS_LINUX)