Remove 'Done' from the schedule_builds cron job

A cron job should be quiet if all goes well. Getting an email that says
'Done' every hour is annoying for administrators.
Merge branch 'quiet-cron' into 'master'

Make the schedule_builds cron job quieter

A cron job should be quiet if all goes well. Getting an email that says
'Done' every hour is annoying for administrators.

See merge request !95