These fields were added to support -merge_pmt_versions, but the mpegts demuxer
is also keeping track its programs internally, so that should be a better place
to handle it.

Also it is not a very good idea to keep fields like program_num or
pmt_stream_idx in an AVStream, because a single stream can be part of multiple
programs, multiple PMTs, so the stream attributes can refer to any program the
stream is part of.

Since they are not part of public API, lets simply remove them, or rather
replace them with placeholders for ABI compatibility with libavdevice.
Signed-off-by: Marton Balint <cus@passwd.hu>