refactor: remove nested orgs labels route

[AlirieGray]

This PR removes an outdated swagger definition for the orgs/orgID/labels route which was not being used, and removes the label handler from the org handler to reflect this change.

Continuation of #19102

• Well-formatted commit messages
• Rebased/mergeable
• Tests pass
• http/swagger.yml updated (if modified Go structs or API)

more of a comment

[glinton]

code looks fine, i'm hesitant to approve as i don't have context regarding the snippet you posted in your other pr. Maybe @ebb-tide would be able to confidently say whether this would have any ill effects or not (tests seem to pass so i'd say ✔️, but they've missed things before)

This code is not behind a feature flag, as the route that this label handler was supporting is not functional currently and is not being used in our UIs. Instead of returning an empty array of labels, this route will now return a 404.

[stephanie-engel]

@AlirieGray @russorat
I noticed that the nested org labels route was removed from OSS, but it still exists (and works) in Cloud 2. Is that to be expected, or should there be another PR to remove that code from Cloud 2

Nvm, I was using an older Cloud 2 cluster that didn't have the latest changes.