Remove unused member ev_producing_event_(SkeletonPipeline)

[lhtin]

The class member ev_producing_event_ of Producer is unused, the 1 cycle delay is configured in Consumer consumer_in_port_ member like below. Removing it to avoid misunderstanding.

class Consumer : public sparta::Unit
{
    // Consumer's InPort to get data
    sparta::DataInPort<uint32_t> consumer_in_port_{&unit_port_set_, "consumer_in_port", 1};
}

[klingaard]

Yeah, I think I had an intention of using this event to show how you can delay internal work in the producer. But we have other examples of that elsewhere.

Thanks for the fix.