Remove mention of mini pipeline graph hover

What does this MR do and why?

Relates to #336741 (closed) and !85298 (merged)

Since we are removing the hover functionality of downstream pipelines in the mini pipeline graph, we no longer need documentation which demonstrates this.

How to set up and validate locally

1. Visit the Multi-project pipelines page
2. Insure that there is no mention of a expand-on-hover feature with a gif at the bottom of the page.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.