Remove links to timeline events from system notes

What does this MR do and why?

Related to #367856 (closed)

Removes anchored links to timeline events from system notes.

System notes and timeline events are located in different tabs of a page ("Summary" vs "Timeline"). At the moment, anchor links do not switch to another tab.

We're planning to reintroduce these links, once we make it possible to switch to another tab.

The initial discussion can be found in the following thread.

Changelog is not needed, the complete feature is behind a feature flag

Screenshots or screen recordings

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