dt-bindings: display: remove backlight node from panel examples

dt-bindings: display: remove backlight node from panel examples

The examples for these panel drivers have a backlight node in addition to
the actual panel node. However the exact backlight is outside the scope of
this binding and should be dropped from the example.

Link: https://lore.kernel.org/linux-devicetree/20230724143152.GA3430423-robh@kernel.org/
Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Acked-by: David Lechner <david@lechnology.com>
Link: https://lore.kernel.org/r/20231011-dt-panel-example-no-backlight-v1-1-b81618d32752@bootlin.com
Signed-off-by: Rob Herring <robh@kernel.org>