Remove known_event files form the codebase

What does this MR do and why?

This MR removes all the files from known_events folder and all the mentions in the documentation regarding using these files.

We dont use separate files for listing event anymore, but using metric definitions to retrieve list of events.

See for example FF removal issue

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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Related to #299453 (closed)