update so nft doesn't allow optional slug, but has to include tokenid

examples/gno.land/r/matijamarjanovic/tokenhub/tokenhub.gno

@@ -44,19 +44,16 @@ func RegisterToken(tokenGetter grc20.TokenGetter, slugs ...string) {
 	grc20reg.Register(tokenGetter, slug)
 }
 
-func RegisterNFT(nftGetter grc721.NFTGetter, slugs ...string) error {
+// TokenId is mandatory for NFTs
+func RegisterNFT(nftGetter grc721.NFTGetter, tokenId string) error {
 	nft := nftGetter()
 	_, ok := nft.(grc721.IGRC721CollectionMetadata)
 	if !ok {
 		return errors.New("NFT must implement IGRC721CollectionMetadata")
 	}
 
 	rlmPath := std.PrevRealm().PkgPath()
-	slug := ""
-	if len(slugs) > 0 {
-		slug = slugs[0]
-	}
-	key := fqname.Construct(rlmPath, slug)
+	key := fqname.Construct(rlmPath, tokenId)
 
 	if registeredNFTs.Has(key) {
 		return ErrNFTAlreadyRegistered