Delete dart2js specific private library code

tool/input_sdk/private/mirror_helper.dart

Index: tool/input_sdk/private/mirror_helper.dart
diff --git a/tool/input_sdk/private/mirror_helper.dart b/tool/input_sdk/private/mirror_helper.dart
index 9c3024fa606840d1b36a5a83fb3a0364134a6698..85cf90677a0a6f104915494c11820067d83bd4e9 100644
--- a/tool/input_sdk/private/mirror_helper.dart
+++ b/tool/input_sdk/private/mirror_helper.dart
@@ -6,20 +6,3 @@
  * changed as a result of compiling with dart2dart.
  */
 library _mirror_helper;
-
-import 'dart:mirrors';
-
-/// The compiler will replace this variable with a map containing all the
-/// renames made in dart2dart.
-const Map<String, String> _SYMBOLS = null;
-
-/// This method is a wrapper for MirrorSystem.getName() and will be inlined and
-/// called in the generated output Dart code.
-String helperGetName(Symbol sym) {
-  var name = MirrorSystem.getName(sym);
-  if (_SYMBOLS.containsKey(name)) {
-    return _SYMBOLS[name];
-  } else {
-    return name;
-  }
-}