SDK / exoplayer

Collapse the two variations of `VorbisUtil.buildMetadata` into a single
method called `VorbisUtil.parseVorbisComments` that only takes a list
of vorbis strings, compared to previously where it would take strings
and picture frame instance. Any code that relied on the old signature
now either concatenates picture frames and vorbis comments or copies
vorbis comments into an existing metadata instance.