Alerting: Remove legacy alerting (#83671)

Removes legacy alerting, so long and thanks for all the fish! 🐟

---------

Co-authored-by: Matthew Jacobson <matthew.jacobson@grafana.com>
Co-authored-by: Sonia Aguilar <soniaAguilarPeiron@users.noreply.github.com>
Co-authored-by: Armand Grillet <armandgrillet@users.noreply.github.com>
Co-authored-by: William Wernert <rwwiv@users.noreply.github.com>
Co-authored-by: Yuri Tseretyan <yuriy.tseretyan@grafana.com>

docs/sources/tutorials/provision-dashboards-and-data-sources/index.md

@@ -68,8 +68,6 @@ provisioning/
     <yaml files>
   dashboards/
     <yaml files>
-  notifiers/
-    <yaml files>
 ```
 
 Next, we'll look at how to provision a data source.