YABEL: Drop IO stubs that are (by own admission) never used

Change-Id: I90a120e64a5062493f64e3e8b48a75dae9342ec4
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/6178
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>