Make deflater constants internal

src/ImageSharp/Formats/Png/Zlib/DeflaterConstants.cs

@@ -3,15 +3,13 @@
 
 // <auto-generated/>
 using System;
-using System.Collections.Generic;
-using System.Text;
 
 namespace SixLabors.ImageSharp.Formats.Png.Zlib
 {
     /// <summary>
     /// This class contains constants used for deflation.
     /// </summary>
-    public static class DeflaterConstants
+    internal static class DeflaterConstants
     {
         /// <summary>
         /// Set to true to enable debugging

src/ImageSharp/Formats/Png/Zlib/DeflaterEngine.cs

@@ -11,7 +11,7 @@ namespace SixLabors.ImageSharp.Formats.Png.Zlib
     /// <summary>
     /// Strategies for deflater
     /// </summary>
-    public enum DeflateStrategy
+    internal enum DeflateStrategy
     {
         /// <summary>
         /// The default strategy