Minor reword of deployment article when using Flex

Author: javiereguiluz

deployment.rst

@@ -132,10 +132,9 @@ How you set environment variables, depends on your setup: they can be set at the
 command line, in your Nginx configuration, or via other methods provided by your
 hosting service.
 
-At the very least you need to define the ``SYMFONY_ENV=prod`` (or
-``APP_ENV=prod`` if you're using :doc:`Symfony Flex </setup/flex>`) to run the
-application in ``prod`` mode, but depending on your application you may need to
-define other env vars too.
+At the very least you need to define the ``APP_ENV=prod`` environment variable
+to run the application in ``prod`` mode, but depending on your application you
+may need to define other env vars too.
 
 C) Install/Update your Vendors
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~