ZTS: Remove TXG_TIMEOUT from dedup_quota test (#17150)

It seems fio in ddt_dedup_vdev_limit overwhelms the system
with the amount of dirty data caused by DDT updates within one
TXG due to tiny 1KB records used, while I see no reason for this
test to extend the TXGs beyond default.

Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: @ImAwsumm
Reviewed-by: Tony Hutter <hutter2@llnl.gov>