Use the actual Country type instead of the name.

We want other pieces of country information (in particular the short
names). This cleans up a lot of code anyway.

As an added bonus, this now catches squadrons that used invalid names
which would previously be passed through to pydcs and... then I don't
know what would happen.

game/ato/flight.py

@@ -37,7 +37,6 @@ class Flight(SidcDescribable):
     def __init__(
         self,
         package: Package,
-        country: str,
         squadron: Squadron,
         count: int,
         flight_type: FlightType,
@@ -49,7 +48,6 @@ class Flight(SidcDescribable):
     ) -> None:
         self.id = uuid.uuid4()
         self.package = package
-        self.country = country
         self.coalition = squadron.coalition
         self.squadron = squadron
         self.squadron.claim_inventory(count)