[FLINK-17658] Rename DefaultTimestampAssigner to RecordTimestampAssigner

flink-core/src/main/java/org/apache/flink/api/common/eventtime/DefaultTimestampAssigner.java → flink-core/src/main/java/org/apache/flink/api/common/eventtime/RecordTimestampAssigner.java

@@ -24,7 +24,7 @@ import org.apache.flink.annotation.Public;
  * A {@link TimestampAssigner} that simply forwards the internal timestamp.
  */
 @Public
-public final class DefaultTimestampAssigner<E> implements TimestampAssigner<E> {
+public final class RecordTimestampAssigner<E> implements TimestampAssigner<E> {
 
 	private static final long serialVersionUID = 1L;