Make calibration fully agnostic to the data's country (no deps on country packages)

[juaristi22]

This will require removing the import of policyengine-us' UCGID in calibrate.py once we have updated the variables for geographic identification in the -us repo.

[juaristi22]

Factors to consider when doing so / deciding how to do so:

Max wanted us to move away from in (the database operation, using equals instead). Ben imagines just a string variable instead of the current Enum will suffice (making the new operation easier to integrate with the current code). However, Ben is currently using the Enum to build the initial hierarchy for the strata (which he thought was a nice source of truth), so we'll have to get it somewhere else if it's no longer an Enum.