Arduino NANO 33 BLE PDM frequency update requested

[facchinm]

Hi Chirp friends :)
We'll soon merge arduino/ArduinoCore-nRF528x-mbedos#33 and release a new version of the Nano 33 BLE core.
As a consequence, the frequency is now exactly 16khz, so the frequency correction code should be removed from the examples

https://github.com/chirp/chirp-arduino/blob/develop/examples/Nano33SenseReceive/Nano33SenseReceive.ino#L152

Cheers,
M