remove generated_sdk from checked in code

test/generated_sdk/lib/core/stacktrace.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.
-
-part of dart.core;
-
-/**
- * An interface implemented by all stack trace objects.
- *
- * A [StackTrace] is intended to convey information to the user about the call
- * sequence that triggered an exception.
- *
- * These objects are created by the runtime, it is not possible to create
- * them programmatically.
- */
-abstract class StackTrace {
-  /**
-   * Returns a [String] representation of the stack trace.
-   *
-   * The string represents the full stack trace starting from
-   * the point where a throw ocurred to the top of the current call sequence.
-   *
-   * The exact format of the string representation is not final.
-   */
-  String toString();
-}
-