Don't pretend Wayland supports Fl::add_system_handler().

src/Fl.cxx

@@ -1050,8 +1050,7 @@ static system_handler_link *sys_handlers = 0;
    - X11: XEvent
    - Windows: MSG
    - OS X: NSEvent
-   - Wayland: NULL (FLTK runs the event handler(s) just before calling \e wl_display_dispatch())
-
+   - Wayland: N/A (Fl::add_system_handler has no effect under Wayland)
  \param ha The event handler function to register
  \param data User data to include on each call
 

src/drivers/Wayland/Fl_Wayland_Screen_Driver.cxx

@@ -1421,12 +1421,8 @@ static const struct wl_registry_listener registry_listener = {
 };
 
 
-extern int fl_send_system_handlers(void *);
-
-
 static void wayland_socket_callback(int fd, struct wl_display *display)
 {
-  if (fl_send_system_handlers(NULL)) return;
   if (wl_display_prepare_read(display) == -1) {
     wl_display_dispatch_pending(display);
     return;