Fixes how to lookup sdk dir to support tests deeper inside test/ folders.

pkg/code_transformers/lib/src/dart_sdk.dart

 // Copyright (c) 2014, 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.
 
 library code_transformers.src.dart_sdk;
 
 import 'dart:convert' as convert;
-import 'dart:io' show Directory, File, Platform, Process;
+import 'dart:io' show File, Platform, Process;
 import 'package:path/path.dart' as path;
 
 
 /// Attempts to provide the current Dart SDK directory.
 ///
 /// This will return null if the SDK cannot be found
 ///
 /// Note that this may not be correct when executing outside of `pub`.
 String get dartSdkDirectory {
 
@@ skipping 21 matching lines @@
 
   var parts = path.split(dartDir);
   // If the dart executable is within the sdk dir then get the root.
   if (parts.contains('dart-sdk')) {
     var dartSdkDir = path.joinAll(parts.take(parts.indexOf('dart-sdk') + 1));
     if (isSdkDir(dartSdkDir)) return dartSdkDir;
   }
 
   return null;
 }
-
-/// Variant of [dartSdkDirectory] which includes additional cases only
-/// typically encountered in Dart's testing environment.
-String get testingDartSdkDirectory {
-  var sdkDir = dartSdkDirectory;
-  if (sdkDir == null) {
-    // If we cannot find the SDK dir, then assume this is being run from Dart's
-    // source directory and this script is the main script.
-    sdkDir = path.join(
-        path.dirname(path.fromUri(Platform.script)), '..', '..', '..', 'sdk');
-  }
-  return sdkDir;
-}