minor #10712 Duplicate composer require in Your First Functional Test chapter (baiolo)

This PR was merged into the 4.1 branch.

Discussion
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Duplicate composer require in Your First Functional Test chapter

The `composer require --dev symfony/browser-kit` command is duplicated at the beginning of _Your First Functional Test chapter_.

Commits
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c39e75b Duplicate composer require in Your First Functional Test chapter

Author: javiereguiluz

testing.rst

@@ -143,13 +143,6 @@ utilities used in the functional tests:
 
 Your First Functional Test
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-First, install the BrowserKit component in your project:
-
-.. code-block:: terminal
-
-    $ composer require --dev symfony/browser-kit
-
 Functional tests are PHP files that typically live in the ``tests/Controller``
 directory for your bundle. If you want to test the pages handled by your
 ``PostController`` class, start by creating a new ``PostControllerTest.php``