[SPARK-11165] Logging trait should be private - not DeveloperApi.

Its classdoc actually says; "NOTE: DO NOT USE this class outside of Spark. It is intended as an internal utility."

Author: Reynold Xin <rxin@databricks.com>

Closes apache#9155 from rxin/private-logging-trait.

core/src/main/scala/org/apache/spark/Logging.scala

@@ -21,19 +21,18 @@ import org.apache.log4j.{LogManager, PropertyConfigurator}
 import org.slf4j.{Logger, LoggerFactory}
 import org.slf4j.impl.StaticLoggerBinder
 
-import org.apache.spark.annotation.DeveloperApi
+import org.apache.spark.annotation.Private
 import org.apache.spark.util.Utils
 
 /**
- * :: DeveloperApi ::
  * Utility trait for classes that want to log data. Creates a SLF4J logger for the class and allows
  * logging messages at different levels using methods that only evaluate parameters lazily if the
  * log level is enabled.
  *
  * NOTE: DO NOT USE this class outside of Spark. It is intended as an internal utility.
  *       This will likely be changed or removed in future releases.
  */
-@DeveloperApi
+@Private
 trait Logging {
   // Make the log field transient so that objects with Logging can
   // be serialized and used on another machine