fix non-field-error duplicate show in model_form

Author: the5fire

xadmin/templates/xadmin/views/model_form.html

@@ -19,7 +19,6 @@
         <button type="button" class="close" data-dismiss="alert">&times;</button>
       {% blocktrans count counter=errors|length %}Please correct the error below.{% plural %}Please correct the errors below.{% endblocktrans %}
       </div>
-      {{ form.non_field_errors }}
   {% endif %}
 
   {% view_block 'before_fieldsets' %}