FCPPluginClient: Change FIXME to not require cleanup of FCPPluginClientTracker since it only keeps WeakReferences to the FCPPluginClients anyway
- So we just need to ensure that the strong references to the FCPPluginClient disappear if the server disappears. Then the FCPPluginClient will be GCed, and thus the WeakReferences will become null at the FCPPluginClientTracker, and it will purge it from its cache using its own ReferenceQueue