rm SolrXMLSerializer, all usage of this class was refactored away a while ago, but it wasn't deleted (merge r1616646)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1616648 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/branches/branch_4x@1616655 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6283: Add support for Interval Faceting in SolrJ

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1616656 13f79535-47bb-0310-9956-ffa450edef68