Check validity of old examples and update or remove them

[chicco785]

1. https://github.com/Atos-Research-and-Innovation/IoTagent-LoRaWAN/tree/master/examples/devices/stm32
2. https://github.com/Atos-Research-and-Innovation/IoTagent-LoRaWAN/tree/master/examples/gateways/picocell
3. https://github.com/Atos-Research-and-Innovation/IoTagent-LoRaWAN/tree/master/examples/stm32_ttn_tutorial