base-files: drop /etc/config/system

The board_detect framework is now able to create the entire system config from
scratch so we can finally drop the copy shipped by base-files.

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

package/base-files/files/etc/config/system

-config system
-	option hostname	lede
-	option timezone	UTC
-	option ttylogin	0
-
-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
-	option enabled 1
-	option enable_server 0