Internal: Remove unnecessary MAILER_DSN env var

Author: AngelFQC

.env.dist

@@ -42,10 +42,6 @@ APP_ENABLE_API_ENTRYPOINT=false
 
 ###< chamilo ###
 
-###> symfony/mailer ###
-# MAILER_DSN='null://null'
-###< symfony/mailer ###
-
 ###> nelmio/cors-bundle ###
 CORS_ALLOW_ORIGIN=^https?://(localhost|127\.0\.0\.1)(:[0-9]+)?$
 ###< nelmio/cors-bundle ###