bug #3648 [Routing] Remove outdated tip about sticky locale (bicpi)

This PR was merged into the 2.3 branch.

Discussion
----------

[Routing] Remove outdated tip about sticky locale

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

Commits
-------

2858786 [Routing] Remove outdated tip about sticky locale

book/routing.rst

@@ -833,11 +833,6 @@ that are special: each adds a unique piece of functionality inside your applicat
 
 * ``_locale``: Used to set the locale on the request (:ref:`read more <book-translation-locale-url>`);
 
-.. tip::
-
-    If you use the ``_locale`` parameter in a route, that value will also
-    be stored on the session so that subsequent requests keep this same locale.
-
 .. index::
    single: Routing; Controllers
    single: Controller; String naming format