AVCodec.pix_fmts is only intended for encoders (decoders use
the get_format callback to let the user choose a pix fmt).
So remove them for the decoders for which this is possible
without further complications; keep them for now in the codecs
that actually use them (by passing avctx->codec->pix_fmts to
ff_get_formatt()).

Also notice that some of these lists were wrong; e.g.
317b7b06 added support for YUV444P16
for cuviddec, but forgot to add it to pix_fmts.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>