Setting them to empty before inheriting copyleft_filter
made them not getting their documented values there.
(From OE-Core rev: ee1f86ca7affc65265f219f0718f89406c9181a5)
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>