Would-be standby-node phoning home every 5 seconds. Why?

PG 14.10

I had initiated streaming replication on a pair of new instances from Node
A to Node B, and then stopped it via:
SELECT pg_terminate_backend(<wallreceiver pid>);
SELECT pg_drop_replication_slot(<slot name>);

That seemed to work, since Node A isn't replicating anymore:

postgres=# SELECT * from pg_replication_slots;
(0 rows)

postgres=#
postgres=# SELECT * from pg_stat_replication;
(0 rows)

Node B, unsurprisingly, doesn't have anything in pg_stat_wal_receiver.
$ psql --host=NodeB -xc "SELECT * FROM pg_stat_wal_receiver;"
(0 rows)

And yet, Node B tries to initialize replication every 5 seconds. An
excerpt from the log file:
2023-12-19 08:53:52.778 EST NodeB replicator 202014 initializing
53300 FATAL: 53300: number of requested standby connections exceeds
max_wal_senders (currently 0)
2023-12-19 08:53:52.778 EST NodeB replicator 202014 initializing
53300 LOCATION: InitProcess, proc.c:358