This script isn't suitable for mt7621 anymore due to switching to DSA
and it needs a different preinit script.
Generic preinit logic in package/base-files has the ability to parse
board.json and pick preinit iface accordingly. Just remove this script
instead of moving it into subtargets.
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
a8d62a4eb1