Fix command response key leak (#1205)

* Fix leaking keys for command response callbacks

* changelog

Author: zeroZshadow

CHANGELOG.md

@@ -19,6 +19,7 @@
 ### Fixed
 
 - Fixed a bug where the Deployment Launcher window would accept tags with 33 characters. [#1202](https://github.com/spatialos/gdk-for-unity/pull/1202)
+- Fixed a small memory leak with command response callbacks using MonoBehaviours. [#1205](https://github.com/spatialos/gdk-for-unity/pull/1205)
 
 ### Internal
 

workers/unity/Packages/io.improbable.gdk.core/Subscriptions/Systems/CommandCallbackSystem.cs

@@ -35,7 +35,7 @@ public ulong RegisterCommandRequestCallback<T>(EntityId entityId, Action<T> call
             return callbacksRegistered++;
         }
 
-        public ulong RegisterCommandResponseCallback<T>(long requestId, Action<T> callback)
+        public void RegisterCommandResponseCallback<T>(long requestId, Action<T> callback)
             where T : struct, IReceivedCommandResponse
         {
             if (!callbackManagers.TryGetManager(typeof(T), out var manager))
@@ -44,9 +44,7 @@ public ulong RegisterCommandResponseCallback<T>(long requestId, Action<T> callba
                 callbackManagers.AddCallbackManager(typeof(T), manager);
             }
 
-            var key = ((CommandResponseCallbackManager<T>) manager).RegisterCallback(requestId, callback);
-            keyToInternalKeyAndManager.Add(callbacksRegistered, (key, manager));
-            return callbacksRegistered++;
+            ((CommandResponseCallbackManager<T>) manager).RegisterCallback(requestId, callback);
         }
 
         public bool UnregisterCommandRequestCallback(ulong callbackKey)