Removed deprecated code

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1634009 13f79535-47bb-0310-9956-ffa450edef68
Refactored message element iterator classes

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1634010 13f79535-47bb-0310-9956-ffa450edef68