Convert CommonVoice test asset to wav, and remove unused test asset (#772)

* converted CommonVoice tartar mp3 to wav using rate 8000 Hz

* Remove Unused dtmf_30s_stereo.mp3

Author: engineerchuan

test/README.md

@@ -85,7 +85,7 @@ Files:
 
 Files:
 
-* `CommonVoice/cv-corpus-4-2019-12-10/tt/clips/common_voice_tt_00000000.mp3`
+* `CommonVoice/cv-corpus-4-2019-12-10/tt/clips/common_voice_tt_00000000.wav`
 * `LibriSpeech/dev-clean/1272/128104/1272-128104-0000.flac`
 * `LJSpeech-1.1/wavs/LJ001-0001.wav`
 * `SpeechCommands/speech_commands_v0.02/go/0a9f9af7_nohash_0.wav`

test/assets/CommonVoice/cv-corpus-4-2019-12-10/tt/clips/common_voice_tt_00000000.mp3

@@ -1,3 +1,3 @@
 client_id	path	sentence	up_votes	down_votes	age	gender	accent
-00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000	common_voice_tt_00000000.mp3	test.	1	0	thirties	female	
-00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001	common_voice_tt_00000000.mp3	test.	1	0	thirties	female	
+00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000	common_voice_tt_00000000.wav	test.	1	0	thirties	female	
+00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001	common_voice_tt_00000000.wav	test.	1	0	thirties	female