lib: cockpit: remove cockpit.when()

Replace the only user of this API with the native Promise equivalent.

This API was never publically documented so nothing should depend on it.

pkg/lib/cockpit.js

@@ -116,12 +116,6 @@ function factory() {
         },
     };
 
-    cockpit.when = function when(value, fulfilled, rejected, updated) {
-        const result = cockpit.defer();
-        result.resolve(value);
-        return result.promise.then(fulfilled, rejected, updated);
-    };
-
     cockpit.defer = function() {
         return new Deferred();
     };

pkg/shell/machines/machines.js

@@ -205,7 +205,7 @@ function Machines() {
         const data = { ...machine, ...values };
         window.sessionStorage.setItem(skey, JSON.stringify(data));
         self.overlay(host, values);
-        return cockpit.when([]);
+        return Promise.resolve([]);
     }
 
     function update_saved_machine(host, values) {