swupdate-image: remove image_types_uboot image class
As of poky commit e18cec7 image_types_uboot.bbclass has been removed and its
features integrated in image_types.bbclass. As a consequence it's no more
needed to include image_types_uboot in the IMAGE_CLASSES.
Signed-off-by: Diego Rondini <diego.rondini@kynetics.com>
Diego Rondini