[PRQ#54241] Deletion Request for ffmpeg21

MarsSeed [1] filed a deletion request for ffmpeg21 [2]: Not useful to keep this legacy ffmpeg from 2013. Buildable, but cannot be executed due to bad packaging. But no longer needed: see deletion requests for its remaining two AUR consumers: - ffdiaporama (PRQ#54124) - x264_152 (PRQ#54125) [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/ffmpeg21/