Summary:
Commit e89d75bc16af0e819a56edd75126ba0ccc42174d changes upstream PG
owned function get_relation_constraint_attnos to take Relation instead
of relation Oid.  This is to be able to call
YBGetFirstLowInvalidAttributeNumber.

There is a YBGetFirstLowInvalidAttributeNumberFromOid.  It was added at
the same time as YBGetFirstLowInvalidAttributeNumber.  So this looks
like an oversight by commit e89d75bc16af0e819a56edd75126ba0ccc42174d.

Change to use YBGetFirstLowInvalidAttributeNumberFromOid, and revert the
extraneous changes to PG owned code.

Jira: DB-16250

Test Plan:
jenkins

Close: #26846

Reviewers: kramanathan

Reviewed By: kramanathan

Subscribers: kramanathan, yql

Differential Revision: https://phorge.dev.yugabyte.com/D43230