clocksource/drivers/arm_global_timer: Remove clockevents shutdown call on offlining

The clockevents core already detached and unregistered it at this stage.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241029125451.54574-7-frederic@kernel.org