minor #8951 use a class based service ID (xabbuh)

This PR was merged into the 3.3 branch.

Discussion
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use a class based service ID

Commits
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9fad2d4 use a class based service ID

Author: javiereguiluz

service_container/factories.rst

@@ -152,8 +152,7 @@ Configuration of the service container then looks like this:
 
         # app/config/services.yml
 
-        app.newsletter_manager:
-            class: AppBundle\Email\NewsletterManager
+        AppBundle\Email\NewsletterManager:
             # new syntax
             factory: 'AppBundle\Email\NewsletterManagerFactory:createNewsletterManager'
             # old syntax