[CLIPTokenizer] Improve warning
Author: patrickvonplaten
Pull request: yes

# What does this PR do?

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As can be seen in this thread the warning is a bit confusing for libraries built on top of `transformes`: https://github.com/huggingface/diffusers/issues/1388#issuecomment-1327760610

Could we maybe downgrade it to a "info" statement and remove the mentioning of BERT? 


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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
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Comments:
_The documentation is not available anymore as the PR was closed or merged._

I feel it's a bit better with a comma or even a period. 

```
"ftfy or spacy is not installed, using custom BasicTokenizer instead of ftfy."
```

I am super motivated to open a PR if you even allow me to just add a comma 😃