devtool: do not write md5sums into upgraded recipes
This will drop them md5sums from recipes that still have them,
and will not re-add them for recipes where they're already
removed.
[RP: Added fix for the test recipe]
Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>