dt-binding: gce: remove thread-num property

"thread-num" is an unused property so we remove it from example.

Signed-off-by: Bibby Hsieh <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>

Documentation/devicetree/bindings/mailbox/mtk-gce.txt

···
 		interrupts = <GIC_SPI 135 IRQ_TYPE_LEVEL_LOW>;
 		clocks = <&infracfg CLK_INFRA_GCE>;
 		clock-names = "gce";
-		thread-num = CMDQ_THR_MAX_COUNT;
 		#mbox-cells = <3>;
 	};