* rootfs_*.bbclass doesn't use this variable anymore, so we can drop it
(From OE-Core rev: bf91547d887aee2893e26e6073e12c540222b422)
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>