some usings cleanup

OpenRA.Game/Traits/Health.cs

@@ -6,16 +6,11 @@
  * as published by the Free Software Foundation. For more information,
  * see LICENSE.
  */
-#endregion
-
-using System;
-using System.Collections.Generic;
-using System.Drawing;
-using System.Linq;
-using OpenRA.Effects;
-using OpenRA.Traits.Activities;
+#endregion
+
+using System.Linq;
+using OpenRA.FileFormats;
 using OpenRA.GameRules;
-using OpenRA.FileFormats;
 
 namespace OpenRA.Traits
 {