dt-bindings: net: renesas,ether: Drop undocumented "micrel,led-mode"

"micrel,led-mode" is not yet documented by a schema. It's irrelevant to
the example, so just drop it.

Signed-off-by: Rob Herring (Arm) <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Conor Dooley <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/devicetree/bindings/net/renesas,ether.yaml

···
             reg = <1>;
             interrupt-parent = <&irqc0>;
             interrupts = <0 IRQ_TYPE_LEVEL_LOW>;
-            micrel,led-mode = <1>;
             reset-gpios = <&gpio5 31 GPIO_ACTIVE_LOW>;
         };
     };