stop building Workstation repo
Similar to what we did for Cloud (6eecb53) we need to stop building
Workstation repos so we can speed up our compose times (see [1]).
We already switched to sourcing from the Everything repo (39683dd).
Now we just need to stop building the repo. This commit makes it so
that we will no longer build the yum repo for Workstation.
[1] https://pagure.io/releng/issue/7403
Signed-off-by: Dusty Mabe <dusty@dustymabe.com>