vaapi: remove unused hw image formats, simplify

PIX_FMT_VDA_VLD and PIX_FMT_VAAPI_VLD were never used anywhere. I'm not
sure why they were even added, and they sound like they are just for
compatibility with XvMC-style decoding, which sucks anyway.

Now that there's only a single vaapi format, remove the
IMGFMT_IS_VAAPI() macro. Also get rid of IMGFMT_IS_VDA(), which was
unused.
vdpau: always let decoder output IMGFMT_VDPAU

The old ffmpeg vdpau support code uses separate vdpau pixel formats for
each decoder (pretty much because mplayer's architecture sucked), which
just gets into the way. Force the old decoder's output to IMGFMT_VDPAU,
and remove IMGFMT_IS_VDPAU() where we can remove it.

This should completely remove the differences betwene the old and new
vdpau decoder outside of the decoder.
gl_hwdec: use a imgfmt field instead of a query_format callback

Now that vdpau always uses a single image format, this can be
simplified.
video: restore printing warning on decreasing filter PTS

Recently, the check was moved, so it was printed only for source video
PTS (since that's easier, and filters should normally behave sane). But
it turns out it's trivial to print a warning in the filter case too by
reusing the code that normally checks for PTS forward jumps without
needing any additional code, so, fine, restore warning in this case.
vf_pullup: properly reset on seek

Sometimes, vf_pullup hanged on seek. This was because it never was
properly reset. Old timestamps messed up the timestamp calculations,
which made the player show frames for a ridiculously long time, which is
perceived as pausing or hanging.