Staging: batman-adv: remove obsoleted vis_format /proc file

batman-adv used to export the vis data using different formats that were
switchable via /proc/net/batman-adv/vis_format. The various formats moved
to user space and rendered this configuration switch useless.

Signed-off-by: Linus Luessing <linus.luessing@web.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>