Delete unused price combi's

_Originally: https://github.com/virge-io/pricelist-frontend/issues/330_

The stuff in #326 : specifies something different.

Stephan complained over the "LONG LIST" of pricecombi's
It's expanding and expanding.

We could easily create a SQL or CLI command script that deletes ALL unused price combi's

That will probably delete over 1000 price combi's.

@Georgi2704 : clear?

For the record: I am not sure if we want this, but happy to discuss this somewhere in an upcoming planning (if we start doing plannings 😄 )