Remove unused function parameter in get_qual_from_partbound

Remove unused function parameter in get_qual_from_partbound

Commit 0563a3a8b changed how partition constraints were generated such
that this function no longer computes the mapping of parent attnos to
child attnos.

This is an external function that extensions could use, so this is
potentially a breaking change. No external callers are known, however,
and this will make it simpler to write such callers in the future.

Author: Hou Zhijie
Reviewed-by: David Rowley, Michael Paquier, Soumyadeep Chakraborty
Discussion: https://www.postgresql.org/message-id/flat/OS0PR01MB5716A75A45BE46101A1B489894379@OS0PR01MB5716.jpnprd01.prod.outlook.com