ublk: don't suggest CONFIG_BLK_DEV_UBLK=Y

ublk: don't suggest CONFIG_BLK_DEV_UBLK=Y

The CONFIG_BLK_DEV_UBLK help text suggests setting the config option to
Y so task_work_add() can be used to dispatch I/O, improving performance.
However, this mechanism was removed in commit 29dc5d06613f2 ("ublk: kill
queuing request by task_work_add"). So remove this paragraph from the
config help text.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Uday Shankar <ushankar@purestorage.com>
Link: https://lore.kernel.org/r/20250416004111.3242817-1-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>