Simplify pipeline code, no unnecessary install of wheel package

[bittner]

The python -m build command executed by Tox takes care of installing the wheel package, which is needed for building a wheel distribution from the source distribution package.

Hence, it's unnecessary to have the wheel package installed by the pipeline, explicitly. Even worse, it creates visual noise, which we want to avoid.

python -m pip install ... is the explicit form of pip install ... when several versions of Python are installed, including their installed version of Pip. If we don't need that type of control we can simply use pip install, which again avoids visual noise that the spectator needs to interpret.