clean up unused custom entered values of fields

I like to have a function for clean up the custem entered values (like location, Group) if the value is´t used anymore.

Example: All Devices moved to a "new" Business location. Old one isn´t used by any device. Now in the Dropdown the "old" location is still availiable. Of course - it´s possible to delete manual. But - there are so much fields that an automatic cleanup would be nice.