mips: dts: ralink: mt7621: remove defining gpio function for pin groups

All pin groups function as gpio unless set otherwise. Therefore, remove
this unnecessary binding.

Tested on UniElec U7621-06-16M on OpenWrt.
Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/dts/ralink/mt7621-gnubee-gb-pc1.dts

@@ -97,18 +97,6 @@ &pcie {
 	status = "okay";
 };
 
-&pinctrl {
-	pinctrl-names = "default";
-	pinctrl-0 = <&state_default>;
-
-	state_default: state-default {
-		gpio-pinmux {
-			groups = "uart3", "wdt";
-			function = "gpio";
-		};
-	};
-};
-
 &gmac1 {
 	status = "okay";
 	phy-handle = <&ethphy4>;

arch/mips/boot/dts/ralink/mt7621-gnubee-gb-pc2.dts

@@ -81,18 +81,6 @@ &pcie {
 	status = "okay";
 };
 
-&pinctrl {
-	pinctrl-names = "default";
-	pinctrl-0 = <&state_default>;
-
-	state_default: state-default {
-		gpio-pinmux {
-			groups = "wdt";
-			function = "gpio";
-		};
-	};
-};
-
 &gmac1 {
 	status = "okay";
 	phy-handle = <&ethphy7>;