dt-binding: gce: remove thread-num property

"thread-num" is an unused property so we remove it from example.
Signed-off-by: Bibby Hsieh <bibby.hsieh@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

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

@@ -39,7 +39,6 @@ Example:
 		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>;
 	};