Removed inapplicable assertion.

Author: bryanedds

Nu/Nu/Core/Xtension.fs

@@ -40,10 +40,6 @@ module Xtension =
         let mutable propertyRef = Unchecked.defaultof<_>
         match UMap.tryGetValue (name, xtension.Properties, &propertyRef) with
         | true ->
-#if DEBUG
-            if property.PropertyType <> propertyRef.PropertyType then
-                failwith "Cannot change the type of an existing Xtension property."
-#endif
             if xtension.Imperative then
                 propertyRef.PropertyValue <- property.PropertyValue
                 struct (true, xtension)