Replace tokenizer class with auto map for relative import of byte tokenizer.

tokenizer_config.json

@@ -1,9 +1,11 @@
 {
   "added_tokens_decoder": {},
+  "auto_map": {
+    "AutoTokenizer": "tokenizer.ByteTokenizer"
+  },
   "byte_level": true,
   "clean_up_tokenization_spaces": true,
   "model_max_length": 1000000000000000019884624838656,
   "padding_side": "left",
-  "tokenizer_class": "ByteTokenizer",
   "truncation_side": "left"
 }