Apparently 1.5 years of warnings isn't enough to get anyone to take any
notice. We therefore make this an error so people can ignore it for
another 6 months whereafter we can finally give up and remove the
obsolete code.
(From OE-Core rev: 0c21d06dea96ca5f19ac2e3136c66da582036a11)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>