Update sox info docstring to account for mp3 frame count handling (#2742)

Summary:
Updates sox info docstring to account for mp3 frame count handling fix introduced in https://github.com/pytorch/audio/issues/2740.

Pull Request resolved: https://github.com/pytorch/audio/pull/2742

Reviewed By: nateanl

Differential Revision: D40189846

Pulled By: nateanl

fbshipit-source-id: d6371418d7d4867dd0b97ee72ebf846d5c93dc30

torchaudio/backend/sox_io_backend.py

@@ -69,7 +69,7 @@ def info(
 
                   * When the input type is file-like object, this function cannot
                     get the correct length (``num_samples``) for certain formats,
-                    such as ``mp3`` and ``vorbis``.
+                    such as ``vorbis``.
                     In this case, the value of ``num_samples`` is ``0``.
                   * This argument is intentionally annotated as ``str`` only due to
                     TorchScript compiler compatibility.