fix: Vocabulary build issue in run_speech_recognition.py
# What does this PR do?
This PR fixes the issue of vocabulary building in run_speech_recognition_ctc.py (https://github.com/huggingface/transformers/blob/master/examples/pytorch/speech-recognition/run_speech_recognition_ctc.py#L332). 

While building vocabulary we replace the blank token " " by pipe symbol as delimiter ("|"). But if the dataset already contains the pipe symbol, which is common in Hindi language as Hindi language uses a similar character "।" as a full stop, in this case we will get two pipe symbols in the vocabulary. This will mess up the further process of creating the dictionary which is adding special tokens. Specifically, the bos token "\<s\>" and the pad token "[PAD]" will get the same index in vocabulary. This will cause the index with [PAD] token to be replaced by \<s\> and the output of Wav2Vec2ForCTC model to contain the "\<s\>" token.   

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Fixes #15275

## Who can review?
@patrickvonplaten , @anton-l , @Narsil
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_15285). All of your documentation changes will be reflected on that endpoint.<|||||>Hey @shivamm7,

Thanks for your issue - I can see the problem. However, instead of deleting `"|"` could you maybe just overwrite:

```
--word_delimiter_token 
```

with a token of your choice? E.g. you could do:

```bash
run_speech_recognition_ctc.py \
  --word_delimiter_token "&"
```

in this case `"&" would be used as the word delimiter token<|||||>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.

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