Staging: brcm80211: remove unused irq typedef

If it's not needed, why define it?

Cc: Brett Rudley <brudley@broadcom.com>
Cc: Henry Ptasinski <henryp@broadcom.com>
Cc: Nohee Ko <noheek@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/staging/brcm80211/include/linuxver.h

@@ -33,9 +33,6 @@
 #include <asm/io.h>
 
 #include <linux/workqueue.h>
-
-typedef irqreturn_t(*FN_ISR) (int irq, void *dev_id, struct pt_regs * ptregs);
-
 #include <linux/sched.h>
 #include <linux/ieee80211.h>