vyatta-cfg-system: revert bb71cf5b7b3a48812e28dbefba8c535f9bbf9973

Reverting commit bb71cf5b7b3a48812e28dbefba8c535f9bbf9973 as it breaks
the logic in vyatta_update_resolv.pl for removing name servers when
called by dhclient-script.  As it stands, the commit causes name server
entries to be left behind in resolv.conf when a DHCP interface is 
deleted, resulting in possibly old or invalid entries remaining 
indefinitely.

Bug #307 http://bugzilla.vyos.net/show_bug.cgi?id=307