Revert FlightDynamics

This needs more thought and most parts might get superseded
by other approaches.

Kept CanSlide separation from CanHover.

OpenRA.Mods.Common/Activities/Air/FlyCircle.cs

@@ -48,7 +48,7 @@ namespace OpenRA.Mods.Common.Activities
 			// We can't possibly turn this fast
 			var desiredFacing = aircraft.Facing + 64;
 
-			// This override is necessary, otherwise aircraft with Slide flag would circle sideways
+			// This override is necessary, otherwise aircraft with CanSlide would circle sideways
 			var move = aircraft.FlyStep(aircraft.Facing);
 
 			Fly.FlyTick(self, aircraft, desiredFacing, aircraft.Info.CruiseAltitude, move, turnSpeedOverride);