Remove deprecated Strings class.

sdk/lib/core/strings.dart

Index: sdk/lib/core/strings.dart
diff --git a/sdk/lib/core/strings.dart b/sdk/lib/core/strings.dart
deleted file mode 100644
index c8a2afc79047a9f79e69bf172ea14729408cccbf..0000000000000000000000000000000000000000
--- a/sdk/lib/core/strings.dart
+++ /dev/null
@@ -1,24 +0,0 @@
-// Copyright (c) 2011, 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;
-
-@deprecated
-abstract class Strings {
-  /**
-   * Joins all the given strings to create a new string.
-   *
-   * *Deprecated* Use `strings.join(separator)` instead.
-   */
-  @deprecated
-  external static String join(Iterable<String> strings, String separator);
-
-  /**
-   * Concatenates all the given strings to create a new string.
-   *
-   * *Deprecated* Use `strings.join()` instead.
-   */
-  @deprecated
-  external static String concatAll(Iterable<String> strings);
-}