Remove superfluous call to notify DCP producer

The core will first process incomming messages (causing {{
DcpProducer::bufferAcknowledgement}} to be called) it'll then call step to process the DCP producer. This happens in the same thread context making the "notify" call as part of executing the ack call superfluous. 
 
If the core spent too much time executing input packets causing the connection to use the entire timeslice before running step, the core will schedule another callback for the connection.