rtc: sh: remove update interrupt handling

Since commit e428c6a2 ("RTC: Clean out UIE icotl implementations"),
the flag for UIE cannot be set anymore. Because UIE is now handled via
regular alarms and a timerqueue by the RTC core, the UIE handling code
can simply go away now.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/20250227134256.9167-12-wsa+renesas@sang-engineering.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>