"BUILD_AOSP_KERNEL=1" is deprecated and only adding "--kernel_package=@//aosp" seems not to for me too ..but I found this in one of the other kernel build scripts and this seems to work: --config=no_download_gki
e.g.: ./build_DEVICE.sh --kernel_package=@//aosp --config=no_download_gki
Clean builds will also not download any prebuilts anymore.