Ensure changes to the SMS period length are noticed

[ChrisD]

Currently if the SMS period (used for SMS accounting purposes) is changed, endroid won't reflect this change even after restart.

It will only take affect when the last period comes to an end
e.g. if the period was 6months, then changed to 1 min followed by an EnDroid restart. Until the initial 6month period expired the new period length would not be noticed.

This is because SMS uses Cron to persist the period timing.

Workaround is to remove the relevant entry in Endroid's cron delay SQL table