remove spurious Clone() from TooltipContainerWidget; all it did was make the error message *worse*

OpenRA.Mods.Cnc/Widgets/TooltipContainerWidget.cs

@@ -64,7 +64,5 @@ namespace OpenRA.Mods.Cnc.Widgets
 		}
 
 		public override string GetCursor(int2 pos) { return null; }
-
-		public override Widget Clone() { throw new NotImplementedException(); }
 	}
 }