sched/headers: Remove the runqueue_is_locked() prototype

Remove the runqueue_is_locked() prototype, the function does not exist anymore.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched.h

@@ -172,8 +172,6 @@ struct uts_namespace;
 
 extern cpumask_var_t cpu_isolated_map;
 
-extern int runqueue_is_locked(int cpu);
-
 extern void scheduler_tick(void);
 
 #define	MAX_SCHEDULE_TIMEOUT	LONG_MAX