Remove dead code: availablePlugins() and *ListPlugins()
availablePlugins is unused except by dbus, and flawed by designed. It makes no sense to have a function that claims to return the list of available plugins, when that list is not complete. You could easily load other plugins from LD_LIBRARY_PATH that availablePlugins doesn't know about. And you could add or remove plugin binaries at runtime which would also invalidate what availablePlugins knows. ListPlugins was only used by availablePlugins.
If you want a list of known plugins, call CompPlugin::getPlugins() instead.