Remove extra windows-char-sanitization, duplicationg and breaking the one in Uri.file.

runtime/bin/builtin.dart

Index: runtime/bin/builtin.dart
diff --git a/runtime/bin/builtin.dart b/runtime/bin/builtin.dart
index 95789889852011c7af5928f390f92d44773deb9b..0ee7575cb178d23c22b1363a63da8b94c900e8a0 100644
--- a/runtime/bin/builtin.dart
+++ b/runtime/bin/builtin.dart
@@ -213,8 +213,6 @@ _extractDriveLetterPrefix(cwd) {
 
 void _setWorkingDirectory(cwd) {
   _workingWindowsDrivePrefix = _extractDriveLetterPrefix(cwd);
-  cwd = _sanitizeWindowsPath(cwd);
-  cwd = _enforceTrailingSlash(cwd);
   _workingDirectoryUri = new Uri.file(cwd);
   if (!_workingDirectoryUri.path.endsWith("/")) {
     var directoryPath = _workingDirectoryUri.path + "/";