The qemu and qemu_uefi_secure images have the same contents as the
qemu_uefi image which wastes space on the release server. A similar
case is the PXE vmlinuz which is the same as the regular one, too.
Set up symlinks for same images, and also detect this when compressing
to set up symlinks there as well. To reduce complexity, the qemu and
qemu_uefi_secure images are not supported anymore and the Jenkins or
GitHub CI will skip over them if specified. Users that build their own
images need to adapt, though.
