MAINTAINERS: relinquish kconfig

Since about the time I was actually added in that file, I've been
almost entirely absent, which totally sucks, and there is no excuse
for my behaviour and for not having relinquished this earlier.

My deepest apologies.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Vincent Legoll <vincent.legoll@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>