Revert[4] of add ImageShader, sharing code with its Bitmap cousin

src/image/SkImage_Gpu.h

Index: src/image/SkImage_Gpu.h
diff --git a/src/image/SkImage_Gpu.h b/src/image/SkImage_Gpu.h
index 5e847dd381cfe657225d67a71007dbd53d3b0a44..8bfdfa7cd834e2fed6260f2dc64cb4f12d5fb952 100644
--- a/src/image/SkImage_Gpu.h
+++ b/src/image/SkImage_Gpu.h
@@ -40,9 +40,6 @@ public:
     SkImage* onNewSubset(const SkIRect&) const override;
 
     GrTexture* peekTexture() const override { return fTexture; }
-    SkShader* onNewShader(SkShader::TileMode,
-                          SkShader::TileMode,
-                          const SkMatrix* localMatrix) const override;
     bool isOpaque() const override;
     bool onReadPixels(const SkImageInfo&, void* dstPixels, size_t dstRowBytes,
                       int srcX, int srcY) const override;