useless argument of ATAddForeignKeyConstraint

Hi,

While reviewing the foreign keys referencing partitioned tables patch, I
noticed that the parentConstr argument of ATAddForeignConstraint is
rendered useless by the following commit:

commit 0325d7a5957ba39a0dce90835ab54a08ab8bf762
Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date:   Fri Jan 18 14:49:40 2019 -0300

    Fix creation of duplicate foreign keys on partitions

Above commit added another function specialized for recursively adding a
given foreign key constraint to partitions, so ATAddForeignConstraint is
no longer called recursively.

Maybe remove that argument in HEAD ?  Attached a patch.

Thanks,
Amit