PrefsPanel::Factory is a specialization of std::function...

... We don't need to define a class for it

src/prefs/ModulePrefs.cpp

@@ -180,8 +180,9 @@ void ModulePrefs::SetModuleStatus(const FilePath &fname, int iStatus){
    gPrefs->Flush();
 }
 
-PrefsPanel *ModulePrefsFactory::operator () (wxWindow *parent, wxWindowID winid)
+PrefsPanel::Factory
+ModulePrefsFactory = [](wxWindow *parent, wxWindowID winid)
 {
    wxASSERT(parent); // to justify safenew
    return safenew ModulePrefs(parent, winid);
-}
+};