Latest single-node CouchDB setup via apt is complete.

I just installed CouchDB via apt on Debian 11. The setup is complete and it seems there is no need for the following line in the documentation:

```
Your installation is not complete. Be sure to complete the [:ref:`Setup `](https://github.com/apache/couchdb-documentation/blob/main/src/install/unix.rst#id7) steps for a single node or clustered installation.
```

Open src/install/unix.rst at the linked single-node setup section and review the installation notice in context. Verify whether the apt installation flow on Debian 11 already completes setup; done means the documentation no longer presents that notice when it is not applicable.

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