[VOL-4548] openonuAdapterGo - memory leak seen in long term tests

Change-Id: I306e3b8d9529ba1ffb43f93cd70524931d7c5e3c
diff --git a/internal/pkg/onuadaptercore/alarm_manager.go b/internal/pkg/onuadaptercore/alarm_manager.go
index 0dbc5b8..2c8690d 100644
--- a/internal/pkg/onuadaptercore/alarm_manager.go
+++ b/internal/pkg/onuadaptercore/alarm_manager.go
@@ -786,3 +786,9 @@
 	am.onuAlarmManagerLock.RUnlock()
 	return value
 }
+
+// PrepareForGarbageCollection - remove references to prepare for garbage collection
+func (am *onuAlarmManager) PrepareForGarbageCollection(ctx context.Context, aDeviceID string) {
+	logger.Debugw(ctx, "prepare for garbage collection", log.Fields{"device-id": aDeviceID})
+	am.pDeviceHandler = nil
+}