While selecting a packet to return to caller in read_packet(), the code
corrects the timestamps for starting timestamps.

However, this is wrong, since for live streams the initial timestamps
might differ just because of the time delay between the retrieval of the
various Media Playlists.

Fortunately, spec 6.2.4 mandates that all variant streams must have
matching timestamps, so we do not need to correct for initial
timestamps.

Drop the correction code.

Note that ID3 timestamps were previously ignored, so this code was
previously actually needed.
Signed-off-by: Anssi Hannula <anssi.hannula@iki.fi>