Revert "ifupdown: create file interfaces if not exist"

This reverts commit 4e692daf.

The patch did not take into consideration of read-only rootfs, causing
the following regression.

  ERROR "The following packages could not be configured offline and rootfs is read-only: ['100-ifupdown']"

The original patch was added to resolve problem running `ifup eth1' on
a systemd based rootfs. However, when using systemd, we do not use ifup
to manage our network interfaces.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>