cpu/hotplug: Remove unused but set variable in _cpu_down()

After the recent removal of the hotplug notifiers the variable 'hasdied' in
_cpu_down() is set but no longer read, leading to the following GCC warning
when building with 'make W=1':

kernel/cpu.c:767:7: warning: variable ‘hasdied’ set but not used [-Wunused-but-set-variable]

Fix it by removing the variable.

Fixes: 530e9b76ae8f ("cpu/hotplug: Remove obsolete cpu hotplug register/unregister functions")
Signed-off-by: Tobias Klauser <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Sebastian Andrzej Siewior <[e-mail]>
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

kernel/cpu.c

···
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 	int prev_state, ret = 0;
-	bool hasdied = false;
 
 	if (num_online_cpus() == 1)
 		return -EBUSY;
···
 		cpuhp_kick_ap_work(cpu);
 	}
 
-	hasdied = prev_state != st->state && st->state == CPUHP_OFFLINE;
 out:
 	cpu_hotplug_done();
 	return ret;