Book: Update link title to match cookbook article title

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | 

Article title updated in c9fe05b3b1a03fa196e80b22472eb3a7eb0be0a5
It'probably better if we just don't use a title here. Then, the referenced article's title will automatically be taken:

```rst
:doc:`/cookbook/bundles/extension`
```