images: Drop explicit libssh2 dependency on opensuse-tumbleweed

This has never been necessary, as the image pre-installs the whole
`cockpit` package, which pulls it in as a dependency. This
build/runtime dependency was dropped in
cockpit-project/cockpit#19441

images/scripts/opensuse-tumbleweed.setup

@@ -26,7 +26,6 @@ glibc-locale \
 glib-networking \
 json-glib \
 kexec-tools \
-libssh2-1 \
 libvirt-daemon-config-network \
 libvirt-daemon-driver-qemu \
 libvirt-daemon-driver-network \