Delete unused BlockQuad struct

src/ImageSharp/Formats/Jpeg/Components/Encoder/BlockQuad.cs

@@ -1,17 +0,0 @@
-// Copyright (c) Six Labors.
-// Licensed under the Apache License, Version 2.0.
-
-namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
-{
-    /// <summary>
-    /// Poor man's stackalloc: Contains a value-type <see cref="float"/> buffer sized for 4 <see cref="Block8x8F"/> instances.
-    /// Useful for decoder/encoder operations allocating a block for each Jpeg component.
-    /// </summary>
-    internal unsafe struct BlockQuad
-    {
-        /// <summary>
-        /// The value-type <see cref="float"/> buffer sized for 4 <see cref="Block8x8F"/> instances.
-        /// </summary>
-        public fixed float Data[4 * Block8x8F.Size];
-    }
-}