Drop inst.stream option and add imgfree

roles/netbootxyz/templates/menu/coreos.ipxe.j2

@@ -27,7 +27,8 @@ goto coreos_exit
 :core_boot
 set base_url ${coreos_mirror}/${coreos_base_dir}
 set build_version ${core_version}
-kernel ${base_url}/${build_version}/x86_64/fedora-coreos-${build_version}-live-kernel-x86_64 ip=dhcp rd.neednet=1 coreos.inst.install_dev=${install_device} coreos.inst.ignition_url=${ignition_url} ${console} coreos.inst.stream=stable initrd=fedora-coreos-${build_version}-live-initramfs.x86_64.img
+imgfree
+kernel ${base_url}/${build_version}/x86_64/fedora-coreos-${build_version}-live-kernel-x86_64 ip=dhcp rd.neednet=1 coreos.inst.install_dev=${install_device} coreos.inst.ignition_url=${ignition_url} ${console} initrd=fedora-coreos-${build_version}-live-initramfs.x86_64.img
 initrd ${base_url}/${build_version}/x86_64/fedora-coreos-${build_version}-live-initramfs.x86_64.img
 boot
 goto coreos_exit