Issue #3303697: Deprecate the optional update system

src/Commands/LightningCoreCommands.php

@@ -37,6 +37,7 @@ class LightningCoreCommands extends DrushCommands {
    *   Runs all available configuration updates.
    */
   public function update() {
+    @trigger_error('The update:lightning command is deprecated in lightning_core:6.0.0 and removed from lightning_core:7.0.0. There is no replacement. See https://www.drupal.org/node/3303698', E_USER_DEPRECATED);
     $io = new DrushStyle($this->input(), $this->output());
     $this->updateManager->executeAllInConsole($io);
   }