fedora: stop building live media with osbuild
Remove the builds for the Fedora Workstation Live Installer with
`osbuild`.
This non-release-blocking artifact has caused some friction and shown
that the current approach by the Image Builder team of building images
through hosted infrastructure is a suboptimal fit for Fedora.
I will be proposing a new way of building images for distributions
hopefully for F42 or F43 at which time this image type might return.
Signed-off-by: Simon de Vlieger <supakeen@redhat.com>