Fix error under KDE+Wayland where keystrokes tend to be repeated

see also: fltk-rs/fltk-rs#1539

src/drivers/Wayland/Fl_Wayland_Screen_Driver.cxx

@@ -770,6 +770,9 @@ static void wl_keyboard_key(void *data, struct wl_keyboard *wl_keyboard,
     }
   } else {
     remove_int_vector(key_vector, for_key_vector);
+    // Under KDE, the time value received doesn't change at each keystroke as it should,
+    // so we remove any key repeat timer at each FL_KEYUP event.
+    Fl::remove_timeout((Fl_Timeout_Handler)key_repeat_timer_cb);
   }
   Fl::e_text = buf;
   Fl::e_length = (int)strlen(buf);