media: amphion: remove unused struct 'vpu_malone_frame_buffer'

'vpu_malone_frame_buffer' has been unused since the original
commit 145e9363 ("media: amphion: implement malone decoder rpc
interface").

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>