Convert to new unit APIs, remove old APIs.

There are probably plenty of raw ints around that never used the old
conversion APIs, but we'll just need to fix those when we see them.

Fixes https://github.com/Khopa/dcs_liberation/issues/558

gen/ato.py

@@ -17,6 +17,7 @@ from typing import Dict, List, Optional
 from dcs.mapping import Point
 
 from game.theater.missiontarget import MissionTarget
+from game.utils import Speed
 from .flights.flight import Flight, FlightType
 from .flights.flightplan import FormationFlightPlan
 
@@ -59,7 +60,7 @@ class Package:
     waypoints: Optional[PackageWaypoints] = field(default=None)
 
     @property
-    def formation_speed(self) -> Optional[int]:
+    def formation_speed(self) -> Optional[Speed]:
         """The speed of the package when in formation.
 
         If none of the flights in the package will join a formation, this