E2E: Remove Unused CODE_SUGGESTIONS Plan

What does this MR do and why?

The CODE_SUGGESTIONS plan is currently not in use by GitLab E2E tests (note: coverage for the Fulfillment-related aspects of code suggestions currently resides only in the CustomersDot project)

This MR removes this plan for now to help avoid confusion and added maintenance until it is needed in the future.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

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How to set up and validate locally

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