Currently, BB_NUMBER_THREADS and PARALLEL_MAKE default to unset and are set in local.conf. Now that we have the automatic probing, the default value of "how many CPUs?" can be moved to bitbake.conf and an example of explicitly defining how many tasks to run can be moved to local.conf.sample.extended.
Fixed in f83319541aad03d4499e1d21940e599ec025547d, part of dizzy.