Add obsoletion to NoSuchDocument as well

Author: RenderMichael

dotnet/src/webdriver/WebDriverResult.cs

@@ -123,6 +123,7 @@ public enum WebDriverResult
         /// <summary>
         /// No document matching the criteria exists.
         /// </summary>
+        [Obsolete("This result is not returned by W3C specifications")]
         NoSuchDocument = 16,
 
         /// <summary>