Deprecate unused interface (#516)

* Addded Obsolete attribute.

Source/DataTypes/ISvgSupportsCoordinateUnits.cs

@@ -1,10 +1,8 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
 
 namespace Svg
 {
+    [Obsolete("ISvgSupportsCoordinateUnits will be removed.")]
     internal interface ISvgSupportsCoordinateUnits
     {
         SvgCoordinateUnits GetUnits();

Source/Painting/SvgGradientServer.cs

@@ -9,7 +9,7 @@ namespace Svg
     /// <summary>
     /// Provides the base class for all paint servers that wish to render a gradient.
     /// </summary>
-    public abstract class SvgGradientServer : SvgPaintServer, ISvgSupportsCoordinateUnits
+    public abstract class SvgGradientServer : SvgPaintServer
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="SvgGradientServer"/> class.
@@ -215,10 +215,5 @@ namespace Svg
 
             return newObj;
         }
-
-        public SvgCoordinateUnits GetUnits()
-        {
-            return GradientUnits;
-        }
     }
 }

Source/Painting/SvgPatternServer.cs

@@ -14,7 +14,7 @@ namespace Svg
     /// A pattern is used to fill or stroke an object using a pre-defined graphic object which can be replicated ("tiled") at fixed intervals in x and y to cover the areas to be painted.
     /// </summary>
     [SvgElement("pattern")]
-    public sealed class SvgPatternServer : SvgPaintServer, ISvgViewPort, ISvgSupportsCoordinateUnits
+    public sealed class SvgPatternServer : SvgPaintServer, ISvgViewPort
     {
         private SvgUnit _x = SvgUnit.None;
         private SvgUnit _y = SvgUnit.None;
@@ -255,10 +255,5 @@ namespace Svg
             return newObj;
 
         }
-
-        public SvgCoordinateUnits GetUnits()
-        {
-            return _patternUnits;
-        }
     }
 }