Clean Alerts with "delete_all"

The destroy_all call was not adequate for the high volume of data, as
instantiates each record in memory.

Delete all executes everything with a single SQL query (what I
originally intended and missed).

app/jobs/delete_old_alert_runs_job.rb

@@ -2,6 +2,6 @@ class DeleteOldAlertRunsJob < ApplicationJob
   queue_as :low
 
   def perform
-    AlertRun.where(run_on: ...1.week.ago).destroy_all
+    AlertRun.where(run_on: ...1.week.ago).delete_all
   end
 end