Revert this commit to enable backups again.

Backups were run every six hours, but due to the huge increase in the 
size of our DB (Docker volume 'etherpad-db' takes 47 GB at this time), 
backups take almost 3h30 to complete, slowing down the entire instance 
during that period.

Cf. https://team.picasoft.net/picasoft/pl/9w6bq59o93npix1m1kzwpwmqxy

X)

Cette fois ça devrait être bon !

> Dotdeb is an extra repository providing up-to-date packages for your 
Debian 8 “Jessie” servers

...and restore via pg_restore.