per #15423 Remove deprecated features from akka-persistence

* remove channels
* remove View
* remove Processor
* collapse the complicated internal state management
  that was spread out between Processor, Eventsourced and Recovery
* remove Recovery trait, this caused some duplication between Eventsourced
  and PersistentView, but but the enhanced PersistentView will not be based
  on recovery infrastructure, and therefore PersistentView code will be replaced anyway
* remove PersistentBatch
* remove LoopMessage
* remove deleteMessages of individual messages
* remove Persistent, PersistentRepr and PersistentImpl are kept
* remove processorId
* update doc sample code
@ktoso @rkuhn note that this is a source incompatible change. It is now mandatory that the user defines the persistenceId. I thought that was what we wanted, but somehow not implemented fully in the deprecation phase.
It was defaulting to the path without address. If you think it's ok, I'll mention it in the migration guide.