XMLにはremoveChild()は無いよ。

/**
 * Copyright mtok ( http://wonderfl.net/user/mtok )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/qqtO
 */

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" applicationComplete="appCompHandler(event)">
    <mx:Script>
    <![CDATA[
    import mx.events.FlexEvent;
    private function appCompHandler(event:FlexEvent):void{
        println("xmlの操作");
        
        var xml:XML = <root>
            <a id="item">some text</a>
            <a>AAAAAAAAAAAAA</a>
            <b>BBBBBBBBBBBBB</b>
            <c>CCCCCCCCCCCCC</c>
        </root>;
        println("--------------");
        println(xml.toString());

        println("");
        println("--------------");
        
        println("属性idを削除する");
        
        delete xml.a.@id;
        println(xml.toString());
        
        println("");
        println("--------------");
        println("要素ｂを削除する");
        
        delete xml.b;
        println(xml.toString());
        
        println("");
        println("--------------");
        println("要素aを削除する。まとめて複数の要素も削除できちゃう");
        
        delete xml.a;
        println(xml.toString());
    }
    
    private function print(str:String):void{
        taOutput.text = taOutput.text.concat(str);    
    }
    private function println(str:String):void{
        print(str);
        print("\n");    
    }
    ]]>
    </mx:Script>
    <mx:TextArea width="100%" height="100%" id="taOutput" ></mx:TextArea>
</mx:Application>