Host cannot be deleted: there are suspended service instances for this host which need to be removed

I experienced this error when I tried to delete unused host in my BizTalk environment:

In my case, there are no suspended service instances for the related host.

After further research, there is subscription related with the host. You can check the subscription in the Subscription table of BizTalkMsgBoxDb:

SELECT *
  FROM [BizTalkMsgBoxDb].[dbo].[Subscription]
  WHERE nvcApplicationName = 'HostName'

If the query result returns row(s), then you have to remove the subscription with the related host. In my case, there is a dynamic send port related with the host. I un-enlist the send port and re-try to remove the host. That's it!