I use bpmn-js since few day so I can make mistake
I think you can't just remove the namespace because it is often (always?) writting in block (like "bpmn:BaseElement", I don't know how to say in english)
so I think you have to remove all the namespaces in bpmn-js,
however in bpmn-moddle/resources/bpmn/json/bpmn.json there is
maybe you can do something with this.