Don't disallow special tokens

[IsaacBreen]

This fixes a tiktoken-related error:

ValueError: Encountered text corresponding to disallowed special token '<|endoftext|>'.
If you want this text to be encoded as a special token, pass it to `allowed_special`, e.g. `allowed_special={'<|endoftext|>', ...}`.
If you want this text to be encoded as normal text, disable the check for this token by passing `disallowed_special=(enc.special_tokens_set - {'<|endoftext|>'})`.
To disable this check for all special tokens, pass `disallowed_special=()`.