[Speech] Move all examples to new audio feature

[patrickvonplaten]

What does this PR do?

This PR makes sure that audio loading uses the new audio feature in all tests. At the same time the dataset "hf-internal-testing/librispeech_asr_dummy" is updated to make use of the new audio feature.

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[LysandreJik]

Great, very clean to leverage the new datasets audio integration! LGTM