Fix incorrect default theme

lib/lvgl/lv_conf.h

@@ -561,7 +561,7 @@
  *----------*/
 
 /*A simple, impressive and very complete theme*/
-#define LV_USE_THEME_DEFAULT 1
+#define LV_USE_THEME_DEFAULT 0
 #if LV_USE_THEME_DEFAULT
 
     /*0: Light mode; 1: Dark mode*/