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

runtime/bin/platform_fuchsia.cc

 // Copyright (c) 2016, 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_FUCHSIA)
 
 #include "bin/platform.h"
 
 #include <string.h>  // NOLINT
@@ skipping 91 matching lines @@
       }
       pathcopy = NULL;
     }
     // Couldn't find it. This causes null to be returned for
     // Platform.resovledExecutable.
     return NULL;
   }
 }
 
 
-bool Platform::AnsiSupported() {
-  return true;
-}
-
-
 void Platform::Exit(int exit_code) {
   exit(exit_code);
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(HOST_OS_FUCHSIA)