Revise VGGish pipeline test again (#3551)

Summary:
Pull Request resolved: https://github.com/pytorch/audio/pull/3551

Restores VGGish pipeline test to be a function rather than class.

Reviewed By: mthrok

Differential Revision: D48236197

fbshipit-source-id: 25ac19d87a7a0964a9c3f7552037cd6c21dc38a9

test/integration_tests/prototype/vggish_pipeline_test.py

-import unittest
-
 import torchaudio
 from torchaudio.prototype.pipelines import VGGISH
 
 
-class VGGishPipelineTest(unittest.TestCase):
-    def test_vggish(self):
-        input_sr = VGGISH.sample_rate
-        input_proc = VGGISH.get_input_processor()
-        model = VGGISH.get_model()
-        path = torchaudio.utils.download_asset("test-assets/Chopin_Ballade_-1_In_G_Minor,_Op._23_excerpt.mp3")
-        waveform, sr = torchaudio.load(path, backend="ffmpeg")
-        waveform = waveform.mean(axis=0)
-        waveform = torchaudio.functional.resample(waveform, sr, input_sr)
-        batch = input_proc(waveform)
-        assert batch.shape == (62, 1, 96, 64)
-        output = model(batch)
-        assert output.shape == (62, 128)
+def test_vggish():
+    input_sr = VGGISH.sample_rate
+    input_proc = VGGISH.get_input_processor()
+    model = VGGISH.get_model()
+    path = torchaudio.utils.download_asset("test-assets/Chopin_Ballade_-1_In_G_Minor,_Op._23_excerpt.mp3")
+    waveform, sr = torchaudio.load(path, backend="ffmpeg")
+    waveform = waveform.mean(axis=0)
+    waveform = torchaudio.functional.resample(waveform, sr, input_sr)
+    batch = input_proc(waveform)
+    assert batch.shape == (62, 1, 96, 64)
+    output = model(batch)
+    assert output.shape == (62, 128)