[DOCS] Cleans up release notes

[KOTungseth]

Cleans up release notes for Elastic Docs v3.

[Copilot]

Pull Request Overview

This PR cleans up and updates the release notes for Elastic Docs v3 by revising navigation titles, headings, and link identifiers as well as reordering the table of contents entries.

• Updated navigation titles and headings in known-issues.md, breaking-changes.md, and release-notes.md
• Revised version identifiers and release dates in breaking-changes.md and release-notes.md
• Removed deprecations.md and updated the table of contents

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
docs/release-notes/known-issues.md	Updated navigation title and added identifier to the header
docs/release-notes/breaking-changes.md	Revised navigation title, header, and updated the release date
docs/release-notes/toc.yml	Updated the table of contents to include release-notes.md as a primary file
docs/release-notes/release-notes.md	Revised header, version identifiers, and headings
docs/release-notes/deprecations.md	File removal

Comments suppressed due to low confidence (1)

docs/release-notes/release-notes.md:24

• The release date in release-notes.md (March 25, 2025) differs from the updated date in breaking-changes.md (April 2, 2025). Please verify and update for consistency.

**Release date:** March 25, 2025

[mergify]

This pull request does not have a backport label. Could you fix it @KOTungseth? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.
• backport-9./d is the label to automatically backport to the 9./d branch. /d is the digit.
• backport-8.x is the label to automatically backport to the 8.x branch.
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-8 is the label that automatically backports to all active minor branches for the 8 major.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[colleenmcginnis]

@KOTungseth I already copied over your edits from elastic/docs-content#827 in #16304. Can we close this?

[mergify]

This pull request is now in conflicts. Could you fix it @KOTungseth? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b docs/rn-cleanup upstream/docs/rn-cleanup
git merge upstream/main
git push upstream docs/rn-cleanup