maintainers.inc: unassign Oleksandr Kravchuk from python3 and all other items

We were not able to get a response about availability over email, and so the recipes
have to be unassigned.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 2d2c7553)
Signed-off-by: Steve Sakoman <steve@sakoman.com>