s390/dasd: remove IOSCHED_DEADLINE from DASD Kconfig

CONFIG_IOSCHED_DEADLINE was removed with
commit f382fb0b ("block: remove legacy IO schedulers")

and setting of the scheduler was removed with
commit a5fd8ddc ("s390/dasd: remove setting of scheduler from driver").

So get rid of the select.

Reported-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>