MDL-58736 core_calendar: Revert calendar_get_events to 3.2 implementation

MDL-58736 core_calendar: Revert calendar_get_events to 3.2 implementation

We modified calendar_get_events in a non backwards compatible way
so instead of fixing that, an easier approch is to simply revert
it to the 3.2 implementation. This should be fine since the way
to get events is going to change in an upcomming release, and we
had to swap all occurences of calendar_get_events in core with
calendar_get_legacy_events to make sure the calendar and overview match.