cpu: Remove try_get_online_cpus()

Now that synchronize_sched_expedited() no longer uses it, there are
no users of try_get_online_cpus() in mainline.  This commit therefore
removes it.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

include/linux/cpu.h

@@ -228,7 +228,6 @@ extern struct bus_type cpu_subsys;
 extern void cpu_hotplug_begin(void);
 extern void cpu_hotplug_done(void);
 extern void get_online_cpus(void);
-extern bool try_get_online_cpus(void);
 extern void put_online_cpus(void);
 extern void cpu_hotplug_disable(void);
 extern void cpu_hotplug_enable(void);
@@ -246,7 +245,6 @@ int cpu_down(unsigned int cpu);
 static inline void cpu_hotplug_begin(void) {}
 static inline void cpu_hotplug_done(void) {}
 #define get_online_cpus()	do { } while (0)
-#define try_get_online_cpus()	true
 #define put_online_cpus()	do { } while (0)
 #define cpu_hotplug_disable()	do { } while (0)
 #define cpu_hotplug_enable()	do { } while (0)

kernel/cpu.c

@@ -102,19 +102,6 @@ void get_online_cpus(void)
 }
 EXPORT_SYMBOL_GPL(get_online_cpus);
 
-bool try_get_online_cpus(void)
-{
-	if (cpu_hotplug.active_writer == current)
-		return true;
-	if (!mutex_trylock(&cpu_hotplug.lock))
-		return false;
-	cpuhp_lock_acquire_tryread();
-	atomic_inc(&cpu_hotplug.refcount);
-	mutex_unlock(&cpu_hotplug.lock);
-	return true;
-}
-EXPORT_SYMBOL_GPL(try_get_online_cpus);
-
 void put_online_cpus(void)
 {
 	int refcount;