ARM: dts: imx6ull-phytec-tauri: Remove invalid property

The 'rs485-rts-active-high' property is not a valid property and is not
documented anywhere.

Remove it to fix the following DT schema warning:

serial@21f0000: Unevaluated properties are not allowed ('rs485-rts-active-high' was unexpected)
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6ull-phytec-tauri.dtsi

@@ -260,7 +260,6 @@ &uart4 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_uart4>;
 	rts-gpios = <&gpio3 2 GPIO_ACTIVE_HIGH>;
-	rs485-rts-active-high;
 	linux,rs485-enabled-at-boot-time;
 	status = "okay";
 };