ONOS-7918 yes, release the reference to the reply

Change-Id: I7428cfb93c6cf0e64ee6f6504121fe706f4dd4f8
diff --git a/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/impl/NetconfSessionMinaImpl.java b/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/impl/NetconfSessionMinaImpl.java
index e73a4c6..03b20e3 100644
--- a/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/impl/NetconfSessionMinaImpl.java
+++ b/protocols/netconf/ctl/src/main/java/org/onosproject/netconf/ctl/impl/NetconfSessionMinaImpl.java
@@ -841,8 +841,8 @@
                         event.getDeviceInfo(), event.getMessagePayload());
                 return;
             }
-            CompletableFuture<String> completedReply =
-                    replies.get(messageId.get()); // remove(..)?
+            // Remove the message as it has been processed.
+            CompletableFuture<String> completedReply = replies.remove(messageId.get());
             if (completedReply != null) {
                 completedReply.complete(event.getMessagePayload());
             }