Delete Sitecore items from remote databases when delete occurs in master.

RemoteDelete.config

<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
  <sitecore>
    <events>
      <event name="item:deleting">
        <handler type="MyProject.MyNamespace.RemoteDeleteHandler, MyProject" method="OnItemDeleting" />
      </event>
    </events>
  </sitecore>
</configuration>

RemoteDeleteHandler.cs

public class RemoteDeleteHandler
{
    protected void OnItemDeleting(object sender, EventArgs args)
    {
        if (!(Event.ExtractParameter(args, 0) is Item deletedItem))
            return;

        if (deletedItem.ID == (ID)null || deletedItem.ID == ID.Null)
            return;

        if (!string.Equals(deletedItem.Database.Name, "master", StringComparison.InvariantCultureIgnoreCase))
            return;

        var targetDatabases = GetTargetDatabases(deletedItem.Database);

        DeleteRemoteItems(deletedItem, targetDatabases);
    }

    private static void DeleteRemoteItems(Item item, IEnumerable<Database> targetDatabases)
    {
        if (item.ParentID == (ID)null || item.ParentID == ID.Null)
            return;

        var deletedItemRemoteEvent = new DeletedItemRemoteEvent(item, item.ParentID);

        foreach (var targetDatabase in targetDatabases)
        {
            var remoteItem = targetDatabase.GetItem(item.ID);

            // item does not exist in target database
            if (remoteItem == null)
                continue;

            remoteItem.Delete();
            targetDatabase.RemoteEvents.Queue.QueueEvent(deletedItemRemoteEvent, true, true);
        }
    }

    private static IEnumerable<Database> GetTargetDatabases(Database contextDatabase)
    {
        Assert.ArgumentNotNull(contextDatabase, nameof(contextDatabase));

        var factoryDatabases = Factory.GetDatabases()
            .Where(db => !string.Equals(db.Name, Sitecore.Constants.CoreDatabaseName, StringComparison.InvariantCultureIgnoreCase))
            .Where(db => !string.Equals(db.Name, contextDatabase.Name, StringComparison.InvariantCultureIgnoreCase))
            .Where(db => db.HasContentItem);

        return factoryDatabases.ToList();
    }
}