When deleting statements, don't expand statements enumerator, as it c…

…an be used directly by RDF::Mutable#delete. Fixes #40.

lib/spira/persistence.rb

@@ -460,7 +460,7 @@ def retrieve_attribute(name, options, sts)
     # Destroy all model data
     # AND non-model data, where this resource is referred to as object.
     def destroy_model_data(*args)
-      if self.class.repository.delete(*statements) && self.class.repository.delete([nil, nil, subject])
+      if self.class.repository.delete(statements) && self.class.repository.delete([nil, nil, subject])
         @destroyed = true
         freeze
       end