Remove unneeded and unused code from XmlItemExporter.
Remove unneeded and unused code from XmlItemExporter.

pawelmhm/scrapy,scrapy/scrapy,starrify/scrapy,pablohoffman/scrapy,pablohoffman/scrapy,pawelmhm/scrapy,elacuesta/scrapy,eLRuLL/scrapy,dangra/scrapy,eLRuLL/scrapy,dangra/scrapy,dangra/scrapy,pawelmhm/scrapy,scrapy/scrapy,elacuesta/scrapy,elacuesta/scrapy,scrapy/scrapy,eLRuLL/scrapy,pablohoffman/scrapy,starrify/scrapy,starrify/scrapy