media: Documentation: v4l: Remove reference to video ops

We no longer have format related callbacks in video ops. Remove the
reference to them.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>