mfd: input: rtc: mc13783: Remove deprecated mc13xxx_irq_ack()

mfd: input: rtc: mc13783: Remove deprecated mc13xxx_irq_ack()

mc13xxx_irq_ack() got deprecated and became dead code with commit
10f9edaeaa30 ("mfd: mc13xxx: Use regmap irq framework for interrupts").
It should be safe to remove it now.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com> # for input
Link: https://lore.kernel.org/r/20250811064358.1659-1-akurz@blala.de
Signed-off-by: Lee Jones <lee@kernel.org>