Removed wrong reference to cookbook

The /cookbook/request/mime_type article does not contain an example to
register a kernel listener since 2.5
minor #4013 Removed wrong reference to cookbook (gquemener)

This PR was merged into the 2.5 branch.

Discussion
----------

Removed wrong reference to cookbook

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.5
| Fixed tickets |

The /cookbook/request/mime_type article does not contain an example to register a kernel listener since 2.5

Commits
-------

b8f27ef Removed wrong reference to cookbook