Stop requiring the pep8 tooling
    
    It was renamed upstream as pycodestyle, and Fedora 32 doesn't have the
    old one any more.
    
    This is only useful to run the Buildstream tests, but we already don't
    run them because some other test dependencies are missing from Fedora.
    
    Buildstream master has already moved to pycodestyle, so we can just wait
    for that to trickle down into Fedora.