Disable value_str

value_str is a way to add text on a button without a separate label.
This saves having an extra label object, but uses more memory and is
removed in LVGL8

src/libs/lv_conf.h

@@ -164,7 +164,7 @@ typedef void* lv_anim_user_data_t;
 #define LV_USE_PATTERN  1
 
 /*1: enable value string drawing on rectangles*/
-#define LV_USE_VALUE_STR    1
+#define LV_USE_VALUE_STR    0
 
 /* 1: Use other blend modes than normal (`LV_BLEND_MODE_...`)*/
 #define LV_USE_BLEND_MODES      0