Remove old template config

https://github.com/sonata-project/SonataAdminBundle/issues/1637

This could result in a BC break for users who have this configuration in their config.yml files. To those users: 
You need to remove the "history_revision" line from your config file. The SonataAdminBundle code no longer uses this template configuration entry, so everything should work fine. If it doesn't it's probably because your own code is using, in which case you need to review it.