Revert "rtc: alarm: Add power-on alarm feature"

This reverts commit 2e1a4aefef66db901f9a906b79e30187f10dbecb.

Power off alarm is not set via alarmtimer now. Remove the changes
of power off alarm's previous design.

CRs-Fixed: 2132189
Change-Id: I0f60bec0d94c93c4f2a89ae86a1b0a0d04aa9e48
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>