hardcoded requirement for US-specific geoids in geodata file

[alsnhll]

There are errors being caused by hard-coding that restricts us to simulating the US. For example inference_slot.R calls flepicommon:load_geodata_file to read the geodata file, but this function is expecting a column to be named “geoid” whereas you’re supposed to be able to name the column anything as long as its specified as nodename in the config. And in the section reading in ground truth data there is also some US specific stuff re fips codes, states etc. We don’t want anything US-specific outside of the get_ground_truth function.

[jcblemai]

Fixed in #62