Draft: Add android-tools as a build req, rm aboot-update as a runtime req

We need android-tools at build time for simg2img and avbtool. aboot-update is not needed as a runtime requirement if we agree to only support ostree images with aboot bootloaders. non-ostree images could continue to be supported with UEFI, grub, etc. android-tools also contains mkbootimg, which could make abootimg an optional build dependency.