batman-adv: remove unused callback from batadv_algo_ops struct

commit d9f179877e50ae2681fe7b0b83e0d9f63b6165ad upstream.

Reported-by: Lars Bußmann <ffsoest@kill-you.net>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
[sven@narfation.org: rewritten commit message to make clear that it is an
 bugfix to an user reported crash]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>