treewide: remove maintainer variable from targets

treewide: remove maintainer variable from targets

There is no such role as target maintainer anymore, one should always
send corresponding changes for the review and anyone from the commiters
is allowed to merge them or eventually use the hand break and NACK them.

Lets make it clear, that it is solely a community doing the maintenance
tasks.

Signed-off-by: Petr Štetiar <ynezz@true.cz>
Acked-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Acked-by: Piotr Dymacz <pepe2k@gmail.com>