Remove SkImageGeneratorUtils. None of this code is used.

src/utils/SkImageGeneratorUtils.h

-/*
- * Copyright 2015 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkImageGeneratorUtils_DEFINED
-#define SkImageGeneratorUtils_DEFINED
-
-#include "SkImageGenerator.h"
-
-class SkImage;
-
-class SkImageGeneratorUtils {
-public:
-    // Returns a generator of the specified dimensions, but will always fail to return anything
-    static SkImageGenerator* NewEmpty(const SkImageInfo&);
-
-    // If the bitmap is mutable, it will make a copy first
-    static SkImageGenerator* NewFromBitmap(const SkBitmap&);
-
-    // Ref's the provided texture, so it had better be const!
-    static SkImageGenerator* NewFromTexture(GrContext*, GrTexture*);
-
-    static SkImageGenerator* NewFromImage(const SkImage*);
-};
-
-#endif