dasd: remove dead code

dasd: remove dead code

Since e443343e509a we haven't had a request_fn attached to
this driver, hence any code inside an if (q->request_fn) is
unreachable.

Fixes: e443343e509a ("s390/dasd: blk-mq conversion")
[sth: Keep and fix the dasd_info->chanq_len counter.]
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Jan Hoeppner <[email protected]>
Signed-off-by: Stefan Haberland <[email protected]>
Tested-by: Ming Lei <[email protected]>
Reviewed-by: Omar Sandoval <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>