esp_vfs_fat_unregister_path() function

- ESP_OK on success - ESP_ERR_INVALID_STATE if FATFS is not registered in VFS

FATFS structure returned by esp_vfs_fat_register is destroyed after this call. Make sure to call f_mount function to unmount it before calling esp_vfs_fat_unregister_ctx. Difference between this function and the one above is that this one will release the correct drive, while the one above will release the last registered one