RTC: Cleanup rtc_class_ops->irq_set_state

With PIE mode interrupts now emulated in generic code via an hrtimer,
no one calls rtc_class_ops->irq_set_state(), so this patch removes it
along with driver implementations.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Alessandro Zummo <a.zummo@towertech.it>
CC: Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br>
CC: rtc-linux@googlegroups.com
Signed-off-by: John Stultz <john.stultz@linaro.org>