Cannot remove elements from web.xml in doWithWebDescriptor

class AGrailsPlugin {
    def doWithWebDescriptor = { xml ->
        def mappingElement = xml.'servlet'
        mappingElement[mappingElement.size() - 1] + {
            'servlet' {
                'servlet-name'('a')
                'servlet-class'('com.discorp.web.AServlet')
            }
        }
    }
}

class BGrailsPlugin {
    def loadAfter = ['a']
    def doWithWebDescriptor = { xml ->
        def mappingElement = xml.'servlet'
        mappingElement[mappingElement.size() - 1] + {
            'servlet' {
                'servlet-name'('b')
                'servlet-class'('com.discorp.web.BServlet')
            }
        }
    }
}

class CGrailsPlugin {
    def loadAfter = ['b']
    def doWithWebDescriptor = { xml ->
        def n = xml.servlet.find { node -> node.'servlet-name'.text() == 'a' }
        n.replaceNode {}
    }
}