Replace AmmoPool lookup methods with properties

And gave the more suitable names while at it.
This is more in line with how we do things in
other places.

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

@@ -60,7 +60,7 @@ namespace OpenRA.Mods.Common.Activities
 				return true;
 
 			return rearmable != null && rearmable.Info.RearmActors.Contains(dest.Info.Name)
-					&& rearmable.RearmableAmmoPools.Any(p => !p.FullAmmo());
+					&& rearmable.RearmableAmmoPools.Any(p => !p.HasFullAmmo);
 		}
 
 		public override bool Tick(Actor self)