This shows how to easily remove Logic App Metric Alerts.
Get-AzMetricAlertRuleV2 -ResourceGroupName 'au-edi-dev-rg' | Remove-AzMetricAlertRuleV2
Why would I want to remove all alert rules? I found that if you delete a logic app and that has alerts rules attached, they don’t get removed too. It is not cool that you get charged for these orphan alert rules.