[ATN] Simplify OpenAPI description; drop undocumented 429 claim

Align with MacPorts/Buildbot review guidance: keep the user-facing
description focused on the product link, and leave rate-limit notes in
the PR body only. The addons-server overview does not publish 429 behavior.

Author: cursoragent

services/atn/atn-base.js

@@ -3,13 +3,8 @@ import { nonNegativeInteger } from '../validators.js'
 import { BaseJsonService } from '../index.js'
 
 const description = `
-[addons.thunderbird.net](https://addons.thunderbird.net) (ATN) publishes extensions for Mozilla Thunderbird.
-
-The ATN API is based on the Mozilla addons-server infrastructure. The
-[addons-server API overview](https://mozilla.github.io/addons-server/topics/api/overview.html)
-does not publish explicit per-endpoint rate limits for read-only addon metadata
-requests. Throttled requests return HTTP 429. This badge issues one GET per render
-to \`https://addons.thunderbird.net/api/v3/addons/addon/{addonId}/\`.
+[addons.thunderbird.net](https://addons.thunderbird.net) (ATN) publishes
+extensions for Mozilla Thunderbird.
 `
 
 const schema = Joi.object({