x86/apic: Remove declaration of unused hw_nmi_is_cpu_stuck

Commit 10f9014912 ("x86: Cleanup hw_nmi.c cruft") removed unused
code in the hw_nmi.c file because of the redesign of the hardlockup
watchdog but left declaration of hw_nmi_is_cpu_stuck in linux/nmi.h,
so remvoe it.

Signed-off-by: Yaowei Bai <baiyaowei@cmss.chinamobile.com>
Link: http://lkml.kernel.org/r/1458697210-3027-1-git-send-email-baiyaowei@cmss.chinamobile.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/nmi.h

@@ -65,7 +65,6 @@ static inline bool trigger_allbutself_cpu_backtrace(void)
 #endif
 
 #ifdef CONFIG_LOCKUP_DETECTOR
-int hw_nmi_is_cpu_stuck(struct pt_regs *);
 u64 hw_nmi_get_sample_period(int watchdog_thresh);
 extern int nmi_watchdog_enabled;
 extern int soft_watchdog_enabled;