Aura LED control not functioning

I am using the [Ultra-Slim Round Fingerprint Sensor](https://www.adafruit.com/product/4750) and having an issue controlling the aura LED. The scanner is working perfectly in all other respects (scanning, enrolling, etc) and the aura LED is working fine it automatic mode. But I need to turn off the blue breathing LED when my device is not ready to scan a fingerprint and I am so-far unable to do so.

The LED control function (set_led) sends and receives ok.
```
SENT: 0xEF 0x01 0xFF 0xFF 0xFF 0xFF 0x01 0x00 0x07 0x35 0x04 0x80 0x01 0x00 0x00 0xC2
RCVD: 0x00
```

If it adds any useful information the `FINGERPRINT_LEDOFF (0x51)` command fails. I am not sure if it is supposed to work on this device because it is not in all versions of the code.

I started a thread in the [Adafruit forum](https://forums.adafruit.com/viewtopic.php?f=19&t=190085) but we were unable to resolve it there.

Start at the library's set_led entry point and inspect how the FINGERPRINT_LEDOFF (0x51) command is represented and sent. Reproduce the reported commands with the Ultra-Slim Round Fingerprint Sensor, consult the linked forum discussion, and consider the issue done when the correct LED-off behavior is established and covered by the library or its documentation.

Written by the indexing model from the issue text.