Spurious pgstat_drop_replslot() call

Hi hackers,

Please find attached a tiny patch to remove a $SUBJECT.

Indeed, it does not seem appropriate to remove stats during slot invalidation as
one could still be interested to look at them.

This spurious call has been introduced in be87200efd. I think that initially we
designed to drop slots when a recovery conflict occurred during logical decoding
on a standby. But we changed our mind to invalidate such a slot instead.

The spurious call is probably due to the initial design but has not been removed.

I don't think it's worth to add a test but can do if one feel the need.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com