fix(slabs): hide top slab items

Registering the top slab block to the ItemBlock.class
rather than the ItemCarvableSlab.class, prevents the top slab items
to show-up in NEI while maintaining compatibility with existing worlds.

src/main/java/team/chisel/Features.java

@@ -3104,6 +3104,6 @@ public enum Features {
 	private static void registerSlabTop(Block bottom, Block top) {
 		String name = Block.blockRegistry.getNameForObject(bottom);
 		name = name.substring(name.indexOf(':') + 1) + "_top";
-		GameRegistry.registerBlock(top, ItemCarvableSlab.class, name);
+		GameRegistry.registerBlock(top, name);
 	}
 }