[Audio Processor] Only pass sr to feat extractor
Author: sanchit-gandhi
Pull request: yes

# What does this PR do?

The audio processor is composed of two components:
1. Feature extractor (input audio -> normalised audio)
2. Tokenizer (target text-> label ids)

Of these two components, the `audio` inputs and `sampling_rate` are arguments that are applicable to the feature extractor only. The `text` is applicable to the tokenizer only.

Currently, we only isolate the `audio` for the feature extractor and `text` for the tokenizer. However, the `sampling_rate` is passed to **both** the feature extractor and tokenizer. Thus, we get a warning for an unrecognized keyword argument in the tokenizer:

```python
from transformers import Wav2Vec2Processor
import numpy as np

audio = np.ones((2, 1000))
text = ['the cat', 'sat on']

processor = Wav2Vec2Processor.from_pretrained('facebook/wav2vec2-base')

out = processor(audio, sampling_rate=16000, text=text)
```

```
Keyword arguments {'sampling_rate': 16000} not recognized.
```

This PR splits the `sampling_rate` from the kwargs and passes it only to the feature extractor.

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Comments:
Currently, I've only applied the change to the Wav2Vec2 Processor - once we're happy with the change I'll copy it to all audio processor classes. I've only done it to this one first to make the review easier!

_The documentation is not available anymore as the PR was closed or merged._