After upgrading to London, Alert action rules are still present in the system. Alert action rules are deprecated in the London release, although they can still be seen in a read-only mode, in the table em_alert_rule. There is an option of migrating one or all these rules to alert management rules.
London and above
At the moment there are no plans to automatically remove these rules, although ServiceNow recommends migrating these rules, to get the benefits of using Alert Management rules. In order to encourage usage of Alert Management Rules, any new rules will only be created as Alert Management rule rather than using the legacy Alert rules.