Allow filtering for rooms with no local users

[schildbach]

Is your feature request related to a problem? Please describe.

I'd like to delete all rooms with zero local users, as they only bloat the database. For this, I need to query a list of those rooms first.

Describe the solution you'd like

A filter option "No local users".

Describe alternatives you've considered

The existing filter option "Empty room" isn't enough. I've got at least one room with zero local users (!ehXvUhWNASUkSLvAGP:matrix.org) that doesn't match the option. It's either because it isn't named "Empty room", or maybe it's because it has remote users.