Do not process psr_3 log messages, as it's now done by symfony.

Related to symfony/symfony#21705

Note: It's not an issue to let monolog doing it, but if monolog do it
symfony can not do it. The best experience is when symfony do it.

So let's disable it.

Author: lyrixx

app/config/config_dev.yml

@@ -20,6 +20,7 @@ monolog:
             channels: ['!event']
         console:
             type:   console
+            process_psr_3_messages: false
             channels: ['!event', '!doctrine', '!console']
         # uncomment to get logging in your browser
         # you may have to allow bigger header sizes in your Web server configuration

app/config/config_prod.yml

@@ -19,3 +19,4 @@ monolog:
             level: debug
         console:
             type: console
+            process_psr_3_messages: false