Remove unused import

Author: cosmo0920

src/main/java/org/fluentd/logger/FluentLoggerFactory.java

@@ -19,7 +19,6 @@
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
-import java.util.Collections;
 import java.util.Map;
 import java.util.Properties;
 import java.util.WeakHashMap;