DeskClock: Fix updating remaining time in timer

When a TimerViewHolder is bound to a Timer, we need to start
TimerFragment$TimeUpdateRunnable to get the remaining time updated
continously.

Previously, if a running timer was not bound to a holder and then became
bound, only the circle animation was running, but the remaining time was
updated just once.

Calling updateTime in TimerViewHolder.onBind is no longer needed, since
TimerFragment$TimeUpdateRunnable will do that via
TimerAdapter.updateTime.

Fixes: https://gitlab.com/LineageOS/issues/android/-/issues/8474
Change-Id: I096605db590d200e8b20f36762bded4d0d32ca79