adm5120: remove target specific /etc/config/system

Now that deviations to the default /etc/config/system are registered via
board.d we can drop the target specific copy.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/adm5120/base-files/etc/config/system

@@ -1,40 +0,0 @@
-config system
-	option hostname	OpenWrt
-	option timezone	UTC
-
-config timeserver ntp
-	list server	0.openwrt.pool.ntp.org
-	list server	1.openwrt.pool.ntp.org
-	list server	2.openwrt.pool.ntp.org
-	list server	3.openwrt.pool.ntp.org
-
-config led
-	option sysfs		lan1
-	option trigger		port_state
-	option port_state	link_act
-
-config led
-	option sysfs		lan2
-	option trigger		port_state
-	option port_state	link_act
-
-config led
-	option sysfs		lan3
-	option trigger		port_state
-	option port_state	link_act
-
-config led
-	option sysfs		lan4
-	option trigger		port_state
-	option port_state	link_act
-
-config led
-	option sysfs		wan
-	option trigger		port_state
-	option port_state	link_act
-
-config led
-	option sysfs		wlan
-	option trigger		netdev
-	option dev		wlan0
-