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>

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;