remove unused import

Author: Vladimir Kotal

opengrok-indexer/src/main/java/org/opengrok/indexer/configuration/Configuration.java

@@ -51,7 +51,6 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.logging.Level;
 import java.util.logging.Logger;
-import java.util.regex.Pattern;
 import java.util.regex.PatternSyntaxException;
 import java.util.stream.Collectors;