LUCENE-6019, LUCENE-6117: remove -Dtests.assert: this is too big a change for a bug-fix release (and it introduced a bug)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_10@1646416 13f79535-47bb-0310-9956-ffa450edef68