Code review comment for ~dashmage/charm-logrotated:bug/2017798-update-cron-daily-location

I see one potential problem now - in an upgrade scenario, even after implementing this fix, the sudo user crontab would still exist if cron-update-daily-schedule was configured. This would mean that the script would still run twice.

I propose that we add a function that checks whether the `/var/spool/cron/crontabs/root` crontab file exists and remove it in case it is present since we are only managing through `/etc/crontab`.