Remove obsolete code.

OpenRA.Game/FieldSaver.cs

@@ -13,7 +13,6 @@ using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Drawing;
-using System.Drawing.Imaging;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
@@ -88,11 +87,6 @@ namespace OpenRA
 				return ((HSLColor)v).ToHexString();
 			}
 
-			if (t == typeof(ImageFormat))
-			{
-				return ((ImageFormat)v).ToString();
-			}
-
 			if (t == typeof(Rectangle))
 			{
 				var r = (Rectangle)v;