Remove vacancy expiration mails

One-sentence description

Remove vacancy expiration mails.

Why?

The vacancy expiration mails are a bit feature creep. They are not really helpful, because the commissioner of external affairs has their own administration with expiration dates (including the vacancies). Furthermore, the emails also don't help because they arrive either too late or too soon. Some partners have a lot longer negotiating time than one month, while others can be handled within a few days.

Besides that, it is also a bit weird that we are only sending mails about vacancies. What about the partner profiles? Why are we not tracking expiration dates for those?

Suggested implementation

I suggest we remove this functionality altogether which will result in less code to maintain and less useless emails to be sent.