Stop saying that we are limited to 24 mirrors

See 0f2cc85 originally. But now our pool is getting a bit too small (see #9022 (closed)), so let’s remove this indication and it might bring a couple more mirrors in play.

Feature Branch: doc/10094-stop-saying-24-mirrors

Related issues

Related to #9022 (closed)

Original created by @sajolida on 10094 (Redmine)

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