Delete openh264 repo definition during repo_setup
    
    This repo is causing problems for Branched update tests. The
    repo is not available for 26 at all yet. This shouldn't be a
    problem as the repo is disabled by default, but it seems that
    some things - at least realmd, as used in the FreeIPA enrolment
    tests - still try to update the repo's metadata when installing
    packages, and fail because it 404s.
    
    Since none of our tests actually needs this repo AFAIK, let's
    just delete it in repo_setup.