Remove rebase requirement for community contribution too behind master

• Please check this box if this contribution uses AI-generated content (including content generated by GitLab Duo features) as outlined in the GitLab DCO & CLA

What does this MR do and why?

The code review guidelines still mentioned that MRs from the community that are 1000+ commits behind master should be rebased before merging.

Thanks to merged result pipelines this is not the case anymore hence the removal of the guideline from the docs, to avoid confusion 🙂

The same thing is mentioned at the very bottom of the Merging a merge request section: https://docs.gitlab.com/ee/development/code_review.html#merging-a-merge-request

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

N.A.

Before	After

How to set up and validate locally

N.A.