Convert Altitude to world coords.

Removes the obsolete AltitudeInit: use CenterPositionInit instead.

OpenRA.Game/ActorInitializer.cs

@@ -55,14 +55,6 @@ namespace OpenRA
 		public int Value( World world ) { return value; }
 	}
 
-	public class AltitudeInit : IActorInit<int>
-	{
-		[FieldFromYamlKey] public readonly int value = 0;
-		public AltitudeInit() { }
-		public AltitudeInit( int init ) { value = init; }
-		public int Value( World world ) { return value; }
-	}
-
 	public class LocationInit : IActorInit<CPos>
 	{
 		[FieldFromYamlKey] public readonly int2 value = int2.Zero;