media: imx: Remove unused functions

Neither imx_media_mbus_fmt_to_ipu_image nor imx_media_ipu_image_to_mbus_fmt
were used anywhere.

Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@puri.sm>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>