How to remove the specific attribute from XmlDocument - c#-4.0

Question

My Xml as below
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<order>
<class>
<about></about>
</class>
<dataset>
<subjects>
<subject>
<addresses>
<address/>
</addresses>
</subject>
</subjects>
</dataset>
</order>
To reorder the xml element and to add namespace i did it as per below:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<order>
<class>
<about></about>
</class>
<dataset>
<subjects>
<subject>
</subject>
</subjects>
<addresses>
<address/>
</addresses>
</dataset>
</order>
I did using below code
XmlNamespaceManager nsmgr = new XmlNamespaceManager(xmlClueReqToLexisNexis.NameTable);
nsmgr.AddNamespace("ab", "http://example.com/abc");
XmlNode order = xmlClueReqToLexisNexis.SelectSingleNode("//ab:order", nsmgr);
XmlNode dataset = xmlClueReqToLexisNexis.SelectSingleNode("//ab:order//ab:dataset", nsmgr);
var subjects = order.SelectSingleNode("//ab:order//ab:dataset//ab:subjects", nsmgr);
I am able to reorder and add namespace to it but it left behind xmlns attribute
as below:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<order>
<class>
<about></about>
</class>
<dataset>
<subjects>
<subject xmlns="">
</subject>
</subjects>
<addresses xmlns="">
<address/>
</addresses>
</dataset>
</order>
I want to remove only attribute xmlns="" out of addresses and subject
Please suggest me the best way to do that.