systemd: Eliminate jQuery from motd card
systemd: Eliminate jQuery from motd card

- Use state variable instead of querying the text from the widget.
 - Drop the unused data-stable attribute.
 - Use arrow instead of function() to eliminate the `self = this` dance.

Closes #13295
martinpitt/cockpit,mvollmer/cockpit,garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpituous/cockpit,garrett/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,deryni/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpit-project/cockpit,garrett/cockpit,cockpit-project/cockpit,deryni/cockpit,martinpitt/cockpit,cockpituous/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,deryni/cockpit,moraleslazaro/cockpit,deryni/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,garrett/cockpit