rtc: remove rtc_set_date

Since it's not defined and used anywhere.

Cc: qemu-trivial@nongnu.org
Signed-off-by: NHu Tao <hutao@cn.fujitsu.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

include/hw/timer/mc146818rtc.h

@@ -9,6 +9,5 @@
 ISADevice *rtc_init(ISABus *bus, int base_year, qemu_irq intercept_irq);
 void rtc_set_memory(ISADevice *dev, int addr, int val);
 int rtc_get_memory(ISADevice *dev, int addr);
-void rtc_set_date(ISADevice *dev, const struct tm *tm);
 
 #endif /* !MC146818RTC_H */