Import `SPIECE_UNDERLINE` from `file_utils` instead of WET definition
Many places define `SPIECE_UNDERLINE` in the code like this: `SPIECE_UNDERLINE = "▁"`

Instead it should me imported: `from transformers.file_utils import SPIECE_UNDERLINE`.

I can provide a PR...
This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>I am still planning to provide a PR later.