After heap_idf.c has been added (where the FreeRTOS heap is a subset of the
ESP-IDF heap), xPortGetFreeHeapSize() was updated to only returns the free
size of the FreeRTOS heap and not the entire ESP-IDF heap.
This commit replaces calls of xPortGetFreeHeapSize() with
esp_get_free_heap_size() in places outside of FreeRTOS.