bblayers.conf.sample: remove BBLAYERS_NON_REMOVABLE
Hob was the only thing paying attention to this, and now Hob itself has
been removed we can remove this as well.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>