Cropping parameters were being miscalculated - getting the output width/height wrong when an x/y crop offset was given. Cropping was also incorrectly being applied twice (because at some point after the convertframe code was written, `videocrop` also started paying attention to the GstVideoCropMeta, but not in useful ways for this purpose). Add a buffer probe to strip the crop meta from the input buffer so videocrop can do its job correctly. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8526>