ata: drop unused ata_id_to_hd_driveid()

This function was renamed from ide_id_to_hd_driveid() and moved from
drivers/ide/ to <linux/ata.h> but it never got used by libata, thus it
became useless after drivers/ide/ removal...

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>