Alerting: Update legacy alerting warning (#66269)

* Update legacy alerting warning

* Apply suggestions from code review

Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

* Update DeprecationNotice.tsx

* silly linter

* Clarify alerting deprecation

---------

Co-authored-by: Gilles De Mey <gilles.de.mey@gmail.com>
Co-authored-by: brendamuir <100768211+brendamuir@users.noreply.github.com>

public/app/features/alerting/components/DeprecationNotice.tsx

@@ -5,23 +5,19 @@ import { Alert } from '@grafana/ui';
 export const LOCAL_STORAGE_KEY = 'grafana.legacyalerting.unifiedalertingpromo';
 
 const DeprecationNotice = () => (
-  <Alert severity="warning" title="Grafana legacy alerting is going away soon">
+  <Alert severity="warning" title="Grafana legacy alerting is deprecated and will be removed in a future release.">
     <p>
-      You are using Grafana legacy alerting, it has been deprecated and will be removed in the next major version of
-      Grafana.
+      You are using Grafana legacy alerting, which has been deprecated since Grafana 9.0. The codebase is now staying as
+      is and will be removed in Grafana 11.0.
       <br />
-      We encourage you to upgrade to the new Grafana Alerting experience.
+      We recommend upgrading to Grafana Alerting as soon as possible.
     </p>
     <p>
       See{' '}
-      <a href="https://grafana.com/docs/grafana/latest/alerting/unified-alerting/difference-old-new/">
-        What’s New with Grafana Alerting
+      <a href="https://grafana.com/docs/grafana/latest/alerting/migrating-alerts/">
+        how to upgrade to Grafana Alerting
       </a>{' '}
-      to learn more about what&lsquo;s new or learn{' '}
-      <a href="https://grafana.com/docs/grafana/latest/alerting/unified-alerting/opt-in/">
-        how to enable the new Grafana Alerting feature
-      </a>
-      .
+      to learn more.
     </p>
   </Alert>
 );