Update var_dumper.rst

DebugBungle is not enabled by default
symfony/symfony#25283

Author: nidzho

components/var_dumper.rst

@@ -80,8 +80,7 @@ DebugBundle and Twig Integration
 --------------------------------
 
 The DebugBundle allows greater integration of the component into the Symfony
-full-stack framework. It is enabled by default in the *dev* and *test*
-environment of the Symfony Standard Edition.
+full-stack framework. 
 
 Since generating (even debug) output in the controller or in the model
 of your application may just break it by e.g. sending HTTP headers or