MetricsRegistry unregister fix.

NioNetworking can be stopped and started. When this happens, the
IOThreads get re-registered and will overwrite the old probes. This
causes logging noise.

This PR fixes this problem by deregistering the IOThreads when NioNetworking
is shutdown.

(cherry picked from commit 4d9c28e)

hazelcast/src/main/java/com/hazelcast/internal/networking/nio/NioNetworking.java

@@ -230,6 +230,7 @@ public void shutdown() {
         shutdown(outputThreads);
         outputThreads = null;
         closeListenerExecutor.shutdown();
+        metricsRegistry.deregister(ioBalancer);
     }
 
     private void shutdown(NioThread[] threads) {
@@ -238,6 +239,7 @@ private void shutdown(NioThread[] threads) {
         }
         for (NioThread thread : threads) {
             thread.shutdown();
+            metricsRegistry.deregister(thread);
         }
     }