Remove unused utility method

util.go

@@ -177,26 +177,6 @@ func flipHorizontal(src *image.NRGBA) *image.NRGBA {
 	return output
 }
 
-func flipVertically(src *image.NRGBA) *image.NRGBA {
-	bounds := src.Bounds()
-	output := image.NewNRGBA(bounds)
-
-	for x := bounds.Min.X; x < bounds.Max.X; x++ {
-		for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
-			index := y*src.Stride + x*4
-			inputColor := src.Pix[index : index+4]
-
-			index = (bounds.Max.Y-y-1)*output.Stride + x*4
-			output.Pix[index] = inputColor[0]
-			output.Pix[index+1] = inputColor[1]
-			output.Pix[index+2] = inputColor[2]
-			output.Pix[index+3] = inputColor[3]
-		}
-	}
-
-	return output
-}
-
 func fixTransparency(img *image.NRGBA) *image.NRGBA {
 	checkColor := img.Pix[0:4]