Remove the message correlation guide from 8.5 and above

[conceptualshark]

Description

Relates to https://github.com/camunda/developer-experience/issues/69

Remove the message correlation guide from versions 8.5 and above.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[conceptualshark]

@christinaausley Updated this to replace the old link to the message correlation section in Message events - I think it should be good to go now.

[akeller]

Thank you. I know we don't enjoy removing guides, but it's the right thing to do in this case. Thanks for adjusting!