Remove insignificant test assets

@astaff had introduced guideline for test assets in https://github.com/pytorch/audio/pull/759 and we can get rid of the following existing assets.

• 100Hz_44100Hz_16bit_05sec.wav sine wave, should be replaced by on-the-fly generation.
• 440Hz_44100Hz_16bit_05sec.wav sine wave, should be replaced by on-the-fly generation.
• CommonVoice/cv-corpus-4-2019-12-10/tt/clips/common_voice_tt_00000000.mp3 whitenoise, should be converted to wav so that test does not require mp3 decoder.
• dtmf_30s_stereo.mp3 not used.
• genres/noise/noise.0000.wav should be replaced by on-the-fly generation.
• kaldi_file.wav sine wave only contains 20 samples and I do not think this is appropriate for test.
• kaldi_file_8000.wav sine wave, should prefer on-the-fly generation.
• sinewave.wav sine wave, should prefer on-the-fly generation.
• steam-train-whistle-daniel_simon.mp3 should be replaced by steam-train-whistle-daniel_simon.wav
• test.wav file generated during test_io.py accidentally checked in
• waves_yesno/0_1_0_1_0_1_1_0.wav
• whitenoise_1min.mp3 should be replaced by on-the-fly generation.
• whitenoise.mp3 should be replaced by on-the-fly generation.
• whitenoise.wav should be replaced by on-the-fly generation.

General Direction for replacing assets with on-the-fly generation

1. Create Tensor

common_utils.get_sinusoid
common_utils.get_whitenoise

2. Get temporary file path

self.get_temp_path('foo.wav')
# suppose this class is composed of `common_utils.TempDirMixin`

3. Save wav file

common_utils.save_wav(path, data)

4. Load wav file

common_utils.load_wav(path)

Search the test suite for kaldi_file.wav, kaldi_file_8000.wav, and sinewave.wav, then inspect the relevant uses of common_utils.get_sinusoid, save_wav, and load_wav. Replace the remaining checked-in assets with temporary, generated WAV files and remove assets that are no longer used; run the affected tests to confirm they still pass.