Use glob in datasets instead of walk_files

[vincentqb]

Replace walk_files+filter in datasets by globing,

• librispeech
• libritts
• speechcommands
• tedlium
• vctk
• yesno

Example (noted in discussion):

walker = sorted(str(p) for p in Path(self._path).glob('*/*_no_hash_*.wav'))

• Once this is done, we can deprecate torchaudio.datasets.utils.walk_files.

cc #910

[faroit]

Shouldn't the globs be sorted for reproducibility reasons?

[vincentqb]

Yes, tests should catch if the order is not consistent, see also comment. (Added sorted() in description above.)

[vincentqb]

Closed by #1109