Handle scrobble deletions across services
Add delete handling for scrobbles: in jetstream handle "delete"
commits for SCROBBLE_NSID by deleting the DB record and publishing a
"rocksky.delete.scrobble" NATS event; add a delete_scrobble helper.
In analytics add on_delete_scrobble to subscribe to that subject and
remove scrobbles from the local DB. Remove an unused NotNull import.