LUCENE-5770: Upgrade to JFlex 1.6, which has direct support for supplementary code points - as a result, ICU4J is no longer used to generate surrogate pairs to augment JFlex scanner specifications.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1608134 13f79535-47bb-0310-9956-ffa450edef68