Remove default compression level test for mp3 (#886)

Author: mthrok

test/torchaudio_unittest/sox_io_backend/save_test.py

@@ -235,7 +235,7 @@ def test_multiple_channels(self, dtype, num_channels):
     @parameterized.expand(list(itertools.product(
         [8000, 16000],
         [1, 2],
-        [None, -4.2, -0.2, 0, 0.2, 96, 128, 160, 192, 224, 256, 320],
+        [-4.2, -0.2, 0, 0.2, 96, 128, 160, 192, 224, 256, 320],
     )), name_func=name_func)
     def test_mp3(self, sample_rate, num_channels, bit_rate):
         """`sox_io_backend.save` can save mp3 format."""