media: dt-bindings: sh-mobile-ceu: Remove now unimplemented bindings documentation

Remove the SH Mobile CEU bindings documentation as the corresponding driver
was removed v5.1 by the following commit:

43a445f1 ("media: sh_mobile_ceu_camera: remove obsolete soc_camera driver")

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>