Cleanup the applehttp as demuxer name, when use the command :

ffmpeg -formats, get the confused information like:
"
 E hls             Apple HTTP Live Streaming
D  hls,applehttp   Apple HTTP Live Streaming
"
we don't use applehttp as the demuxer/muxer name usually, so
cleanup the applehttp and update the documents.

After the change, get the information from "ffmpeg -formats":
"
DE hls             Apple HTTP Live Streaming
"
Reviewed-by: Steven Liu <lq@onvideo.cn>
Signed-off-by: Jun Zhao <barryjzhao@tencent.com>