SOLR-6597: Removed SolrIndexConfig parameter from one of the SolrIndexSearcher constructor, where it was never really used (merge from trunk r1629772)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1629784 13f79535-47bb-0310-9956-ffa450edef68