koji_builder: drop local site config to add /dev/fuse
    
    We added local site config to make sure there was a /dev/fuse in the
    mock nspawn container in order to get ostree oci image building working
    correctly. Now in mock 5.x, /dev/fuse is automatically setup/added, so
    we need to drop our local config so it doesn't conflict with the
    internal upstream version now.
    
    See: https://github.com/rpm-software-management/mock/issues/1188
    
    Signed-off-by: Kevin Fenzi <kevin@scrye.com>