ESP32Cam Face Detection crash fix

Reference:

【(不成功来打我)解决esp32cam一人脸检测识别就卡顿终止死机终极必杀！-哔哩哔哩】 https://b23.tv/r16OgXm

https://techtutorialsx.com/2020/06/13/esp32-camera-face-detection/

https://github.com/espressif/arduino-esp32/issues/5128

 app_httpd.cpp

line 286-290, line 389-392 , replace free() to dl_lib_free()

        // free(net_boxes->score);

        // free(net_boxes->box);

        // free(net_boxes->landmark);

        // free(net_boxes);

        dl_lib_free(net_boxes->score);

        dl_lib_free(net_boxes->box);

        dl_lib_free(net_boxes->landmark);

        dl_lib_free(net_boxes);