ipa-upgradeconfig: Remove backed up smb.conf
    
    Since we are not able to properly restore the Samba server to the
    working state after running ipa-adtrust-install, we should not keep
    the smb.conf in the fstore.
    
    This patch makes sure that any backed up smb.conf is removed from
    the backup and that this file is not backed up anymore.
    
    Part of: https://fedorahosted.org/freeipa/ticket/3479