media: dt-bindings: rcar-vin: Remove paragraph about aliases

It might be convenient to have aliases but it's not required, drop the
sentence as it's not true and not used in Gen3 DTS files.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>