remove unused import

Author: Vladimir Kotal

opengrok-indexer/src/test/java/org/opengrok/indexer/history/FileHistoryCacheTest.java

@@ -45,7 +45,6 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
-import java.util.TreeMap;
 
 import org.apache.commons.lang3.time.DateUtils;
 import org.eclipse.jgit.api.Git;