minor #1123 Update testing.rst (yourwebmaker)

This PR was submitted for the master branch but it was merged into the 1.2 branch instead (closes #1123).

Discussion
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Update testing.rst

Actually there is no "Reusing applications" topic on Usage chapter.

Commits
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4cb970b8 Update testing.rst

doc/testing.rst

@@ -71,11 +71,6 @@ use it by making your test extend it::
         ...
     }
 
-.. note::
-
-    To make your application testable, you need to make sure you follow "Reusing
-    applications" instructions from :doc:`usage`.
-
 .. note::
 
     If you want to use the Symfony2 ``WebTestCase`` class you will need to