atmel-demo-image: remove useless remove_kernel_rootfs_postprocess
atmel-demo-image: remove useless remove_kernel_rootfs_postprocess

remove_kernel_rootfs_postprocess is not needed because the kernel is not
installed by default, thanks to RDEPENDS_kernel-base="" in the kernel
recipe.

Signed-off-by: Alexandre Belloni <a7228e626ecf0022ac91fc1cd8db88e71d0e5e0e@free-electrons.com>

kraj/meta-atmel,linux4sam/meta-atmel,linux4sam/meta-atmel,linux4sam/meta-atmel,alexandrebelloni/meta-atmel,alexandrebelloni/meta-atmel,kraj/meta-atmel,alexandrebelloni/meta-atmel,linux4sam/meta-atmel,linux4sam/meta-atmel,kraj/meta-atmel