[Refactor] remove unused code (#6879)

fe/fe-core/src/main/java/org/apache/doris/catalog/Database.java

@@ -76,10 +76,6 @@ import java.util.stream.Collectors;
 public class Database extends MetaObject implements Writable {
     private static final Logger LOG = LogManager.getLogger(Database.class);
 
-    // empirical value.
-    // assume that the time a lock is held by thread is less than 100ms
-    public static final long TRY_LOCK_TIMEOUT_MS = 100L;
-
     private long id;
     private volatile String fullQualifiedName;
     private String clusterName;