fix: remove obsolete Arduino authentication configuration

[dido18]

The auth configuration of the apt-repo can be removed.

At the time of writing endpoints apt-repo.oniudra.cc and apt-repo.arduino.cc are still protected by basic auth.

WAIT devops to remove basic auth before merging

How to test:

After basic auth remoed from `apt-repo.oniudra?

change the config of a board as follows:

• remove the etc/apt/auth.conf.d/arduino.conf
• change the /etc/apt/sources.list.d/arduino.list and put deb [signed-by=/etc/apt/keyrings/arduino.asc] https://apt-repo.oniudra.cc/ stable main
• exceuete apt update

Expected: no 401 error