oxnas: drop explicit pre-init iface

According to Jonas Gorski this is no longer needed, the problem
originally addressed by first adding 07_preinit_iface and subsequently
merging that into 02_network was probably a bug during the transition
to the new board.d pre-init approach.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/oxnas/base-files/etc/board.d/02_network

@@ -5,8 +5,6 @@
 
 board_config_update
 
-ifname=eth0
-
 ucidef_set_interface_lan "eth0" "dhcp"
 
 board_config_flush