Move filtering of past events in related events section to backend

Category: Bug Fix/Enhancement

This MR added the filtering of past events in the related events section. This code was added in the frontend. Normally event queries have a filter pipe in the backend. A function to filter past (or future) events is already present there. Furthermore, list_related_events only returns the first 4 related_events. If these are all past events, the related events section will be empty, even if other future events exist.

Change: revert the MR and instead use the filter_future_events function in the backend

Alternative: keep the current implementation

Benefits: increased maintainability/mentioned bug won't occur