Add "cleanup" to the deployment script

[mowtschan]

Is your feature request related to a problem? Please describe.
If you try to deploy firmware with ./Firmware/ESP32/flash_esp32.sh
and it fails, you need to remove tmp.key file manually before you can run the script again.

Describe the solution you'd like
I would like to have a kind of "cleanup" in ./Firmware/ESP32/flash_esp32.sh:

cleanup() {
    echo "cleanup ..."
    rm -v "$KEYFILE"
}
...
set -e
trap cleanup INT TERM EXIT
...

[Sn0wfreezeDev]

At the moment the deployment script is mainly built to run from our app, which always removes the entire directory when finished.
You can make a pull request with this function for the manual installation and I'm happy to accept it.

[mowtschan]

Should be fixed with PR #46