Also make the GroupHost plugin type agnostic

src/wine-host/bridges/vst2.h

@@ -78,11 +78,6 @@ class Vst2Bridge : public HostBridge {
      */
     std::optional<VstTimeInfo> time_info;
 
-    /**
-     * The path to the .dll being loaded in the Wine VST host.
-     */
-    const boost::filesystem::path vst_plugin_path;
-
    private:
     /**
      * A wrapper around `plugin->dispatcher` that handles the opening and