Super sidebar: Remove super_sidebar_before

What does this MR do and why?

With the recent introduction of replace_placeholder we have more granular control over the order of menu items in a panel. This commit removes the last use of super_sidebar_before (has no impact on the order) and all the codre related to it.

Screenshots or screen recordings

Before	After

(Or is before after or after before? 😆 You can tell that order stayed the same, so woop woop)

How to set up and validate locally

Not needed, I think.

MR acceptance checklist

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