Comment # 6 on bug 1123534 from Dominique Leuenberger

the control.xml comes from the package skelcd-control-openSUSE, which packages

/usr/lib/skelcd/CD1/control.xml

skelcd-control-openSUSE is already a dependency to
installation-images:openSUSE, where the control.xml is copied into
skelcd-installer-openSUSE.rpm

so I think the easiest solution would be to simply remove
skelcd-control-openSUSE from the media creation meta package list, and rely on
the skelcd-installer-* bringing the right packages / control files