oxnas: remove uboot-oxnas-ox820 from default package selection

All supported boards should work with the $vendor bootloader just fine.
Existing users should mindfully re-flash using new initramfs build and
restore $vendor bootloader's bootcmd to it's original setting.

Signed-off-by: Daniel Golle <[email protected]>

target/linux/oxnas/ox820/target.mk

@@ -3,10 +3,6 @@ BOARDNAME:=OX820/NAS782x
 CPU_TYPE:=mpcore
 FEATURES+=nand pci pcie ubifs usb
 
-DEFAULT_PACKAGES += \
-	uboot-oxnas-ox820
-
-
 define Target/Description
     Oxford/PLXTECH OX820/NAS782x
 endef