Thanks glebfm@ for noticing that Simply (an m-p-d product)
takes no kernel inside squashfs but relies on livecd-install's
50-restore-kernel.sh hook to copy the kernel from iso9660
and regenerate initrd (which is a must anyways but requires
System.map to be still around).

This saves about 3 Mb in ISO size for a LiveCD using
kernel-image-std-def-4.1.15-alt1.x86_64.rpm.