[Wav2Vec2ProcessorWithLM] improve decoder download
Author: patrickvonplaten
Pull request: yes

# What does this PR do?

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This PR significantly speeds up the `.from_pretrained(...)` method of `Wav2Vec2ProcessorWithLM`. 

Currently the tests will fail. They should pass as soon as https://github.com/huggingface/huggingface_hub/commit/010db7570ffaa131666a000189c6c3962aa24e32 released.


## Before submitting
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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
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Library:

- benchmarks: @patrickvonplaten
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- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

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Comments:
Not super urgent the PR - would be good to be merged by early/mid next week.

Just released version v0.4.0 for `huggingface_hub` - reran the test suite, everything passes. 

Merging!