Remove excess clearing

src/ImageSharp/Formats/Tiff/Compression/Compressors/PackBitsCompressor.cs

@@ -29,7 +29,6 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Compression.Compressors
             DebugGuard.IsTrue(rows.Length % height == 0, "Invalid height");
             DebugGuard.IsTrue(this.BytesPerRow == rows.Length / height, "The widths must match");
 
-            this.pixelData.Clear();
             Span<byte> span = this.pixelData.GetSpan();
             for (int i = 0; i < height; i++)
             {

src/ImageSharp/Formats/Tiff/Writers/TiffBiColorWriter.cs

@@ -41,8 +41,6 @@ namespace SixLabors.ImageSharp.Formats.Experimental.Tiff.Writers
                 this.pixelsAsGray = this.MemoryAllocator.Allocate<byte>(height * this.Image.Width);
             }
 
-            this.pixelsAsGray.Clear();
-
             Span<byte> pixelAsGraySpan = this.pixelsAsGray.Slice(0, height * this.Image.Width);
 
             Span<TPixel> pixels = GetStripPixels(this.imageBlackWhite.GetRootFramePixelBuffer(), y, height);