Delete element with a specific attribute

As i said in the title :

I want to delete the whole element when i do not get "preRequisite" in the attribute:

(XML) First Element:

  <dependency>
     <dependentAssembly dependencyType="install">
     </dependentAssembly>
  </dependency>

(XML) Second Element:

<dependency>
     <dependentAssembly dependencyType="preRequisite">
     </dependentAssembly>
  </dependency>

Current Code:

private void Deletepopulates(string filepath)
    {
        XmlDocument doc = new XmlDocument();
        doc.Load(filepath);
        foreach(var nodeToDelete in new List<XmlNode>(doc.SelectNodes(filepath + "[@dependencyType!='preRequisite']").Cast<XmlNode>()))
        {
            if (nodeToDelete != null)
            {
                nodeToDelete.ParentNode.RemoveChild(nodeToDelete);
            }
        doc.Save(filepath);
        }
    }

Current it does only delete the Child (dependencyType) but it shall delete the element (dependency), is there a way to delete dependency ?

and at: new List<XmlNode>(doc.SelectNodes(filepath + "[@dependencyType!=preRequisite").Cast<XmlNode>())i get an Exception called: System.Xml.XPath.XPathException

Hopfully its clear otherwhise i'll edit it in your fovor :)