Remove ip_netmask from option parser
    
    ipa-dns-install uses ip_netmask=False --> parse_netmask=False, other installers uses default (parse_netmask=True).
    Use this consistent accross all installers.
    
    Also this option is unused (and shouldn't be used).
    
    https://pagure.io/freeipa/issue/4317
    
    Reviewed-By: David Kupka <dkupka@redhat.com>