Please try to set the action to disable:
Set-AzureRmSqlDatabaseAuditing `
-State Disabled `
-ResourceGroupName "resourcegroupname" `
-ServerName "ssqlinstancename" ` #ssqlinstancename.database.windows.net
-StorageAccountName "strageaccountname" `
-DatabaseName "dbname" `
-AuditActionGroup 'SCHEMA_OBJECT_CHANGE_GROUP' `
-RetentionInDays 8 `
-AuditAction "DELETE ON schema::dbo BY [public]"