chore: eliminate registerTests cmake module (from project-template)

This module is used in this one instance only, hence there is no justification to make it part of the project-template. The module is a lot more complicated than necessary (partialy due to the flawed attempt to make it generic). Simplifiction and cleanup can be done in a separate step.

Note: The project does not compile on Ubuntu 20.04, but it does not do so even without these modifications!

requested review from @martin.killenberg

assigned to @martin.killenberg

The MCU firmware needs the ARM toolchain. We cannot simply build it with dragon at the moment. Unfortunately it already does not work properly on Ubuntu20.04 any more. It produces broken binaries.

approved this merge request

merged