rootfs_ipk: delete opkg metadata if package management not required and all packages are configured
If all the postinsts were successfully run in offline mode, and
package-management hasn't been requested as an IMAGE_FEATURE, the opkg
metadata is now redundant and can safely be deleted.
Also, the update-rc.d and base-passwd packages can be removed since
they will serve no further purpose in this situation.
If some packages are still unconfigured at this point then we need to
keep their metadata around so that either opkg or the awk script can
configure the packages at boot time. In theory it would be possible to
strip out the data for packages that have already been configured, but
right now we just hold on to the whole status file in that situation.
