Drop some config options that are no longer used.
WARNING: Config option release_is_layered was removed and has no effect;
remove it. It's layered if there's configuration for base product.
WARNING: Config option runroot was removed and has no effect; remove it.
Please specify 'runroot_method' if you want to enable runroot, otherwise run
things locally.
WARNING: Config option bootable was removed and has no effect; remove it.
Setting buildinstall_method option if you want a bootable installer.
Signed-off-by: Kevin Fenzi <kevin@scrye.com>