Docs Fix - git_abuse_rate_limit_feature_flag cleanup happened in 15.11 (not 15.10)

What does this MR do?

The FF git_abuse_rate_limit_feature_flag clean up was not merged in v15.10 but with v15.11. This docs is causing confusion to the customers. Correcting the release version info.

(Requests to amend the milestones in the related issue and MR have been raised already:

• !113934 (comment 1420179581)
• #394996 (comment 1420178117)

Related issues

#394996 (closed)

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
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  • Style Guide.
• If you're adding or changing the main heading of the page (H1), ensure that the product tier badge is added.
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• ~"frontend"
• ~"backend"
• ~"type::bug"
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These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

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If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
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  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.