`unknown_cache` table seems unused and/or redundant

there is a table `unknown_cache` that is touched in the same celery task as the materialized view refresh.

A bunch of the code surrounding it is unused or legacy in one way or another, this cache rebuild seems to be the only place in the code that uses this table.

It is
a) probably not supposed to be in the main data schema since it seems operational
b) probably not needed anymore