bug symfony#4765 [Book][Forms] avoid the request service where possible (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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[Book][Forms] avoid the request service where possible

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

Commits
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a6e1a28 avoid the request service where possible

Author: wouterj

book/forms.rst

@@ -1854,7 +1854,7 @@ an array.
     You can also access POST values (in this case "name") directly through
     the request object, like so::
 
-        $this->get('request')->request->get('name');
+        $request->request->get('name');
 
     Be advised, however, that in most cases using the ``getData()`` method is
     a better choice, since it returns the data (usually an object) after