Remove CCI badge from README (#3420)

Summary:
CI jobs are migrated from CCI to GHA

Pull Request resolved: https://github.com/pytorch/audio/pull/3420

Differential Revision: D46548562

Pulled By: mthrok

fbshipit-source-id: d7e17201e8b256efaa54543e445a0f139aa549b2

README.md

 torchaudio: an audio library for PyTorch
 ========================================
 
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