rm SolrXMLSerializer, all usage of this class was refactored away a while ago, but it wasn't deleted

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1616646 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6336: DistributedQueue can easily create too many ZooKeeper Watches. (closes #80)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1616654 13f79535-47bb-0310-9956-ffa450edef68