Revert changes to shellspout, since gostorms handling of skipped task id...

This change reverts the changes I made in #5.

I submitted a [fix to gostorm](https://github.com/jsgilmore/gostorm/pull/10) for handling the undocumented "need_task_ids" field of the multilang protocol, which removes the need for us to require task_ids for spouts/bolts.

This will also allow us to re-enable the event_receiver bolt in the topology.