Revert "Core/Calendar: Fix memory leak when malformed CMSG_CALENDAR_ADD_EVENT is received"

This partially reverts commit 51e38872c72e16bb0f09e660c2660759021b2176.
The stack-initialized variable calendarEvent would have called CalendarMgr::FreeEventId() when it went out of scope, marking the current event id as free and allowing next event to overwrite current event.
This doesn't fix the memory leak issue which still needs to be addressed in a proper way.