cdrom: remove the unused driver specific disc change ioctl

This was only used by the ide-cd driver, which went away in
commit b7fb14d3ac63 ("ide: remove the legacy ide driver")
so we might as well take advantage of that and get rid of
this hook as well.

Cc: Christoph Hellwig <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Phillip Potter <[e-mail]>
Signed-off-by: Paul Gortmaker <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]
Signed-off-by: Phillip Potter <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

Documentation/cdrom/cdrom-standard.rst

···
 		int (*tray_move)(struct cdrom_device_info *, int);
 		int (*lock_door)(struct cdrom_device_info *, int);
 		int (*select_speed)(struct cdrom_device_info *, int);
-		int (*select_disc)(struct cdrom_device_info *, int);
 		int (*get_last_session) (struct cdrom_device_info *,
 					 struct cdrom_multisession *);
 		int (*get_mcn)(struct cdrom_device_info *, struct cdrom_mcn *);
···
 this `auto-selection` capability, the decision should be made on the
 current disc loaded and the return value should be positive. A negative
 return value indicates an error.
-
-::
-
-	int select_disc(struct cdrom_device_info *cdi, int number)
-
-If the drive can store multiple discs (a juke-box) this function
-will perform disc selection. It should return the number of the
-selected disc on success, a negative value on error. Currently, only
-the ide-cd driver supports this functionality.
 
 ::
 

drivers/cdrom/cdrom.c

···
 			return -EINVAL;
 	}
 
-	/*
-	 * ->select_disc is a hook to allow a driver-specific way of
-	 * seleting disc.  However, since there is no equivalent hook for
-	 * cdrom_slot_status this may not actually be useful...
-	 */
-	if (cdi->ops->select_disc)
-		return cdi->ops->select_disc(cdi, arg);
-
 	cd_dbg(CD_CHANGER, "Using generic cdrom_select_disc()\n");
 	return cdrom_select_disc(cdi, arg);
 }

include/linux/cdrom.h

···
 	int (*tray_move) (struct cdrom_device_info *, int);
 	int (*lock_door) (struct cdrom_device_info *, int);
 	int (*select_speed) (struct cdrom_device_info *, int);
-	int (*select_disc) (struct cdrom_device_info *, int);
 	int (*get_last_session) (struct cdrom_device_info *,
 				 struct cdrom_multisession *);
 	int (*get_mcn) (struct cdrom_device_info *,