qemuarm64-secureboot: don't set append in extlinux.conf
There's no need to set append in the extlinux.conf, as the kernel will
pull the settings passed from runqemu via the DeviceTree.
By explicitly setting append here the kernel doesn't look in the DT, and
the extlinux.conf hardcoded a TAP network configuration which meant that
networking fails for runqemu using slirp.
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>
Ross Burton