remove unnecessary warnings

Author: zhongkechen

sdk/src/main/java/software/amazon/lambda/durable/operation/BaseDurableOperation.java

@@ -204,7 +204,7 @@ protected Operation waitForOperationCompletion() {
                 // strictly before the execution thread (Step or child context) is deregistered.
                 // chain them together
                 future = completionFuture.thenRun(() -> {
-                    logger.warn(
+                    logger.trace(
                             "registering thread {} when operation {} ({}) completed ({})",
                             threadContext.threadId(),
                             getOperation(),