Revert "Change dart:io Platform.script to return a Uri."

tests/standalone/io/file_read_special_device_test.dart

 // Copyright (c) 2013, 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.
 
 import 'package:expect/expect.dart';
 import 'package:path/path.dart';
 import 'dart:io';
 
 void openAndWriteScript(String script) {
-  script = Platform.script.resolve(script).toFilePath();
+  script = join(dirname(Platform.script), script);
   var executable = Platform.executable;
   var file = script;  // Use script as file.
   Process.start("bash", ["-c", "$executable $script < $file"]).then((process) {
     process.exitCode
         .then((exitCode) {
           Expect.equals(0, exitCode);
         });
   });
 }
 
 void testReadStdio() {
   openAndWriteScript("file_read_stdio_script.dart");
 }
 
 void main() {
   // Special unix devices do not exist on Windows.
   if (Platform.operatingSystem != 'windows') {
     testReadStdio();
   }
 }