media: atomisp: Remove unused ia_css_frame_*() functions

After the conversion to videobuf2 a bunch of ia_css_frame_*()
functions are unused, remove them.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>