Change the signature of pgstat_report_vacuum() so that it's passed a Relation

Hi hackers,

While working on relfilenode statistics, Andres suggested that we pass the Relation
to pgstat_report_vacuum() (instead of the parameters inherited from the Relation,
(See [1])).

That looks like a good idea to me as it reduces the number of parameters and it's
consistent with pgstat_report_analyze().

PFA a patch to $SUBJECT.

Thoughts?

[1]: https://www.postgresql.org/message-id/ezbfcpjtfh3vtm667aegyrptcdsvinbuxw6y5p6j3e5fbffrl5@i7v6cjapz3yv

Regards,

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