[Speech Recognition] - Distributed training: Make sure vocab file removal and creation don't interfer 
Author: patrickvonplaten
Pull request: yes

# What does this PR do?

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Correct vocab dict issue with mulit-processing


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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Models:

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Library:

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- tokenizers: @n1t0, @LysandreJik
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- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

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