dt-bindings: arm: rockchip: remove reference to fennec board

The rk3288 fennec board has been removed, remove the binding document at
the same time.
Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip.yaml

@@ -459,11 +459,6 @@ properties:
               - rockchip,rk3288-evb-rk808
           - const: rockchip,rk3288
 
-      - description: Rockchip RK3288 Fennec
-        items:
-          - const: rockchip,rk3288-fennec
-          - const: rockchip,rk3288
-
       - description: Rockchip RK3328 Evaluation board
         items:
           - const: rockchip,rk3328-evb