Workstation & Silverblue: Remove Flathub remote & third party repos
    
    Remove the requirement on fedora-flathub-remote and
    fedora-workstation-repositories for Workstation and Silverblue
    to let users manully remove them post installation.
    
    Those two packages are still installed by default in both Editions
    via the following changes:
    
    - https://pagure.io/fedora-comps/pull-request/789
    - https://pagure.io/workstation-ostree-config/pull-request/337
    
    See also the discussion in:
    
    - https://github.com/fedora-silverblue/issue-tracker/issues/379
    - https://src.fedoraproject.org/rpms/fedora-release/pull-request/232