avformat/hlsenc: fix bug of hlsenc http delete old segments

when push hls to http server, the old segemnts can not delete by hls formats.
so add the http option into hls_delete_old_segments

Reported-by: Yin Jiaoyuan <yinjiaoyuan@163.com>
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>