Cleanup preferred event selection flow chart
As initially mentioned in !579 (comment 110978) the preferred event selection flow chart (https://gwcelery.readthedocs.io/en/latest/gwcelery.tasks.superevents.html#selection-of-the-preferred-event) can be cleaned up by:
- Renaming "Are the events from different search groups?" -> "Are there CBC events"
- Yes -> "Select the events with the greatest number of detectors"
- No -> "Select the event with the lowest FAR"
- Remove the "Select the CBC event" and "From which search group are the events?" elements