Remove SkBitmapAlphaThresholdShader

include/effects/SkBitmapAlphaThresholdShader.h

-/*
- * Copyright 2013 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#include "SkShader.h"
-#include "SkBitmap.h"
-#include "SkRegion.h"
-#include "SkString.h"
-
-class SK_API SkBitmapAlphaThresholdShader : public SkShader {
-public:
-    /**
-     * Creates a shader that samples a bitmap and a region. If the sample is inside the region
-     * the alpha of the bitmap color is boosted up to a threshold value. If it is
-     * outside the region then the bitmap alpha is decreased to the threshold value.
-     * The 0,0 point of the region corresponds to the upper left corner of the bitmap
-     * Currently, this only has a GPU implementation, doesn't respect the paint's bitmap
-     * filter setting, and always uses clamp mode.
-     */
-    static SkShader* Create(const SkBitmap& bitmap, const SkRegion& region, U8CPU threshold);
-};