Remove not needed image parameter from CalculateBitDepth

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -227,12 +227,12 @@ namespace SixLabors.ImageSharp.Formats.Png
             if (this.options.MakeTransparentBlack)
             {
                 quantized = PngEncoderOptionsHelpers.CreateQuantizedFrame(this.options, clonedImage);
-                this.bitDepth = PngEncoderOptionsHelpers.CalculateBitDepth(this.options, clonedImage, quantized);
+                this.bitDepth = PngEncoderOptionsHelpers.CalculateBitDepth(this.options, quantized);
             }
             else
             {
                 quantized = PngEncoderOptionsHelpers.CreateQuantizedFrame(this.options, image);
-                this.bitDepth = PngEncoderOptionsHelpers.CalculateBitDepth(this.options, image, quantized);
+                this.bitDepth = PngEncoderOptionsHelpers.CalculateBitDepth(this.options, quantized);
             }
 
             return quantized;

src/ImageSharp/Formats/Png/PngEncoderOptionsHelpers.cs

@@ -89,11 +89,9 @@ namespace SixLabors.ImageSharp.Formats.Png
         /// </summary>
         /// <typeparam name="TPixel">The type of the pixel.</typeparam>
         /// <param name="options">The options.</param>
-        /// <param name="image">The image.</param>
         /// <param name="quantizedFrame">The quantized frame.</param>
         public static byte CalculateBitDepth<TPixel>(
             PngEncoderOptions options,
-            Image<TPixel> image,
             IndexedImageFrame<TPixel> quantizedFrame)
             where TPixel : unmanaged, IPixel<TPixel>
         {