maintainers.inc: unassign Zang Ruochen

maintainers.inc: unassign Zang Ruochen

There hasn't been any version updates or other oe-core
activity in a long time.

We're actually getting better and timelier updates when
someone sees a recipe has no maintainer and then goes ahead
with the update themselves.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>