Remove dummy filtered slot implementation since it is no longer required

src/main/kotlin/ru/dbotthepony/mc/otm/container/IFilteredContainerSlot.kt

@@ -25,11 +25,4 @@ interface IFilteredContainerSlot : IContainerSlot {
 			return filter === item
 		}
 	}
-
-	@Deprecated("Dummy implementation")
-	class Dummy(parent: IContainerSlot) : IFilteredContainerSlot, IContainerSlot by parent {
-		override var filter: Item?
-			get() = null
-			set(value) {}
-	}
 }