minor #6080 Removed doc about getting original parameter value from ParameterBag (edefimov)

This PR was submitted for the 3.0 branch but it was merged into the 2.8 branch instead (closes #6080).

Discussion
----------

Removed doc about getting original parameter value from ParameterBag

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 3.0
| Fixed tickets |
This PR removes information about getting original parameter value using the third argument of ParameterBag::get() method.

Commits
-------

1e1ecc4 Removed doc about getting original parameter value from ParameterBag

Author: xabbuh

Diff for: components/http_foundation/introduction.rst

@@ -151,22 +151,15 @@ exist::
 
 When PHP imports the request query, it handles request parameters like
 ``foo[bar]=bar`` in a special way as it creates an array. So you can get the
-``foo`` parameter and you will get back an array with a ``bar`` element. But
-sometimes, you might want to get the value for the "original" parameter name:
-``foo[bar]``. This is possible with all the ``ParameterBag`` getters like
-:method:`Symfony\\Component\\HttpFoundation\\Request::get` via the third
-argument::
+``foo`` parameter and you will get back an array with a ``bar`` element::
 
     // the query string is '?foo[bar]=bar'
 
     $request->query->get('foo');
     // returns array('bar' => 'bar')
 
     $request->query->get('foo[bar]');
-    // returns null
-
-    $request->query->get('foo[bar]', null, true);
-    // returns 'bar'
+    // returns null   
 
 .. _component-foundation-attributes: