issue #4223: remove hls_acodec and hls_vcodec config.

[suzp1984]

try to fix #4223

The hls.hls_acodec and hls.hls_vcodec seems meanless, can be removed.

How to verify?

1. objs/srs -c conf/hls.conf

2. publish three kinds of streams: pure audio stream, pure video stream, audio&video stream.
   ffmpeg -re -i doc/source.flv -c copy -vn -f flv rtmp://localhost/live/audio
ffmpeg -re -i doc/source.flv -c copy -an -f flv rtmp://localhost/live/video
ffmpeg -re -i doc/source.flv -c copy -f flv rtmp://localhost/live/av

3. use ffprobe to detect the hls streams.
   ffprobe http://localhost:8080/live/audio.m3u8
ffprobe http://localhost:8080/live/video.m3u8
ffprobe http://localhost:8080/live/av.m3u8

[duiniuluantanqin]

maybe you need check it with Safari on macOS again.

[suzp1984]

maybe you need check it with Safari on macOS again.

checked on safari, access http://localhost:8080/players/srs_player.html?schema=http
play the three hls streams mentioned in step 3:

http://localhost:8080/live/audio.m3u8
http://localhost:8080/live/video.m3u8
http://localhost:8080/live/av.m3u8

everything seems fine.