mxs: drop removal of firewall4 package

Drop removal of firewall4 package for I2SE Duckbill device.

With OPKG the firewall4 package was installed anyway as it's a
dependency of luci-app-firewall and was silently installed again later
in such condition. Drop it to fix support for APK.

Signed-off-by: Christian Marangi <[email protected]>

target/linux/mxs/image/Makefile

@@ -46,7 +46,7 @@ endef
 define Device/i2se_duckbill
   DEVICE_VENDOR := I2SE
   DEVICE_MODEL := Duckbill
-  DEVICE_PACKAGES := -dnsmasq -firewall4 -ppp -ip6tables -iptables -mtd \
+  DEVICE_PACKAGES := -dnsmasq -ppp -ip6tables -iptables -mtd \
 		     uboot-envtools kmod-leds-gpio -kmod-nf-nathelper
   SUPPORTED_DEVICES:=i2se,duckbill
   SOC:=imx28