hlsdemux2: Limit amount of HLSTimeMap stored
Right now the HLSTimeMap list is only cleared when the element is resetted.
It might be good to figure out a way to limit the amount stored. Like only keep the last n-th.
When updating from playlists, look at the first DSN, keep from N before that one.
Also make it an array (instead of a list) while at it.