x86: remove duplicate declaration of unknown_nmi_panic

Signed-off-by: NFernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/asm-x86/nmi.h

@@ -46,7 +46,6 @@ extern void nmi_watchdog_default(void);
 
 extern int check_nmi_watchdog(void);
 extern int nmi_watchdog_enabled;
-extern int unknown_nmi_panic;
 extern int avail_to_resrv_perfctr_nmi_bit(unsigned int);
 extern int avail_to_resrv_perfctr_nmi(unsigned int);
 extern int reserve_perfctr_nmi(unsigned int);