net: remove last dependency on ifcfg persistence

Up until now, some of the most corner case behavior (removal of
partially broken networks) was only working for ifcfg persistence
or ifcfg configurator + unified persistence.

This patch cleans the api from ifcfgisms.

Change-Id: Ia5d682eaf93b488fac0391bf4b84394d73d7f485
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28530
Reviewed-by: Dan Kenigsberg <danken@redhat.com>