test: Drop obsolete MD5 fingerprint fallback
test: Drop obsolete MD5 fingerprint fallback

All our supported OSes have supported SHA256 fingerprints for a while.

martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit