[WCM] Remove URL trailing slash redirect cookbook entry

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | none

To be merged when https://github.com/symfony/symfony-docs/pull/3180 is merged

Discussed [here](https://github.com/symfony-cmf/symfony-cmf-docs/pull/323)