Remove Staging Geo instance scenario

What does this MR do and why?

Staging Geo was removed in gitlab-org/quality/staging!100 (diffs)

There was a pipeline schedule but it has been inactive for 2 years.

See https://gitlab.slack.com/archives/C3JJET4Q6/p1718717210523239 for slack discussion.

Screenshots or screen recordings

n/a

How to set up and validate locally

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

n/a

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• Commits include Changelog: trailer
• I have evaluated the MR acceptance checklist for this MR.