When calculating the audio pts, mpv multiplies the ao delay by the
current audio speed and subtracts it from the written audio pts. This
doesn't really make sense though. mpctx->video_pts is never affected by
the playback speed, and this leads to weird behavior like the audio-pts
property changing values while paused merely because the playback speed
changes. Remove the multiplication and simply subtract the delay by a
factor of 1 instead. When updating the av_diff in player/video, this
does actually need to take in account the audio speed so we do the
calculation there.