use `get_attname` due to dead of `get_relid_attribute_name` on pg 11.
use `get_attname` due to dead of `get_relid_attribute_name` on pg 11.

komamitsu/treasuredata_fdw,komamitsu/treasuredata_fdw,komamitsu/treasuredata_fdw,komamitsu/treasuredata_fdw,komamitsu/treasuredata_fdw