batman-adv: Drop unused headers in trace.h

The commit 9abc291812 ("batman-adv: tracing: Use the new __vstring()
helper") removed the usage of WARN_ON_ONCE and __dynamic_array in this
file. But it was forgotten to adjust the headers accordingly (dropping the
now no longer used ones).

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/trace.h

@@ -9,8 +9,6 @@
 
 #include "main.h"
 
-#include <linux/bug.h>
-#include <linux/kernel.h>
 #include <linux/netdevice.h>
 #include <linux/percpu.h>
 #include <linux/printk.h>