Venue#force_geocoding= was always geocoding

An unchecked checkbox in rails sends the value `"0"`, which is truthy, causing `Venue#force_geocoding=` to always force the geocoding. Ideally, I think there'd be some sort of automatic value coercion to boolean going on here, a la Virtus, but for now, let's just fix the bug.

Also, remove a redundant and duplicated version of the same method from the controller, while we're at it.