media: am437x: remove unused struct vpfe_pixel_format

struct vpfe_pixel_format was defined, but never used. Remove it.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>