selftests: ublk: remove ublk queue self-defined flags

Remove ublk queue self-defined flags, and use the uapi flags directly.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250713143415.2857561-15-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>