dns: Delete dnsNode objects when they are empty

If an update leaves the dnsNode without any entries, the dnsNode object
should be deleted. Thanks to Günter Kukkukk for his excellent debugging
work on this one.

This should fix bug #9559

Signed-off-by: Kai Blin <kai@samba.org>

Reviewed-by: Andrew Bartlett <abartlet@samba.org>
libcli: Remove uneeded debug message

Signed-off-by: Kai Blin <kai@samba.org>

Reviewed-by: Andrew Bartlett <abartlet@samba.org>
WHATSNEW: Fix 4.0 default for allow dns updates.

Reviewed-by: Andrew Bartlett <abartlet@samba.org>
docs: Avoid mentioning a possibly misleading option.

Reviewed-by: Andrew Bartlett <abartlet@samba.org>
param_table: Remove misleading allow dns updates options.

Reviewed-by: Andrew Bartlett <abartlet@samba.org>

Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Sat Jun  1 12:46:32 CEST 2013 on sn-devel-104