remove (empty) SkXfermode.h

BUG=skia:

Change-Id: Ic5ceb829a80252b35d4a953dc32417db9ddc8ec8
Reviewed-on: https://skia-review.googlesource.com/5481
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/include/core/SkXfermode.h b/include/core/SkXfermode.h
deleted file mode 100644
index 199dff2..0000000
--- a/include/core/SkXfermode.h
+++ /dev/null
@@ -1,13 +0,0 @@
-/*
- * Copyright 2006 The Android Open Source Project
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkXfermode_DEFINED
-#define SkXfermode_DEFINED
-
-//#error "SkXfermode.h is deprecated"
-
-#endif