Fix remaining reference to deleted class FredPluginFCPServer:
- Sorry, had forgotten to grep for this. All should be gone now.
- Side note: Yes, it is a bit strange to have two classes freenet.node.fcp.FCPPluginMessage and freenet.pluginmanager.FredPluginFCPMessageHandler:FCPPluginMessage representing the same thing. However conceptually, the requirements of a class representing it is different from the perspective of the low level network FCP interface, and from the client/server side message handling functions. The client/server side handlers need less low level data, and more verbose JavaDoc, so its good to have a small self-contained version of the class in ther FredPluginFCPMessageHandler interface.