Remove Debian 11 (bullseye) support

[martignoni]

Debian 11 (bullseye) was released 4 years ago, in August 2021. Full Debian support lasted until August 14th, 2024. The last RPiOS image based on Debian 11 was published more than 2 years ago, in May 2023.

With Debian 13 (trixie) release, support of Debian 11 (bullseye) will be discontinued.

[martignoni]

Tasks:

• Remove deprecated shell script changewifisettings.sh
• Remove support for old network stack