Update PipeDataRegionAssigner.java

Author: Caideyipi

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/extractor/dataregion/realtime/assigner/PipeDataRegionAssigner.java

@@ -189,6 +189,8 @@ public boolean notMoreExtractorNeededToBeAssigned() {
   // use synchronized here for completely preventing reference count leaks under extreme thread
   // scheduling when closing
   public synchronized void close() {
+    PipeAssignerMetrics.getInstance().deregister(dataRegionId);
+
     final long startTime = System.currentTimeMillis();
     disruptor.shutdown();
     matcher.clear();