Send the database ID of the last replicated item (i.e. `server.replicas_eldb`) to replica

[zuiderkwast]

This is a mistake. The intended behavior was to send the database ID of the last replicated item (i.e. server.replicas_eldb).
It hasn't caused any issues so far, as primary is resetting it in replicationSetupReplicaForFullResync:

valkey/src/replication.c

Line 820 in 838ba44

server.replicas_eldb = -1;

for each new replica.
I will address this in a separate PR.

Originally posted by @naglera in #1609 (comment)