ath79: WNDR3700 v1/v2: make u-boot env partition writable

Remove read-only flag from U-boot environment partition for Netgear
WNDR3700 v1 and v2 so u-boot-envtools can modify data there.

Signed-off-by: Michal Cieslakiewicz <michal.cieslakiewicz@wp.pl>
(cherry picked from commit 6227c8d1bf41739586969c3102897a7ba179114d)

target/linux/ath79/dts/ar7161_netgear_wndr3700.dts

@@ -18,7 +18,6 @@
 	partition@50000 {
 		label = "u-boot-env";
 		reg = <0x050000 0x020000>;
-		read-only;
 	};
 
 	partition@70000 {

target/linux/ath79/dts/ar7161_netgear_wndr3700v2.dts

@@ -18,7 +18,6 @@
 	partition@50000 {
 		label = "u-boot-env";
 		reg = <0x050000 0x020000>;
-		read-only;
 	};
 
 	partition@70000 {