Dear David L 930
Good day!
Thank you for posting to Microsoft Community. We are glad to assist!
Based on your description, I understand you concern that when we deleted the message, deleted message appeared as "This message has been deleted" (as per below screenshot) and you want to remove this space or want to permanently delete message.

We understand your requirement that it will reserve space in your teams channels but for "This message has been deleted", we have only one option available and its “Undo”. Many times accidently users are deleted message and they want to recover it, so at this moment our Product Teams has only set “Undo” option for recover message.
I do apologize that Microsoft Teams doesn't have an option to disable the "undo" function for message deletion.
In the meanwhile, we do understand your concern about this feature that how it helps you to improve your efficiency in such daily busy work schedule but as it is related with Teams product design, so it is suggested to submit your valuable feedback directly to Microsoft product development team by either go to Help from your dedicated App > submit Feedback or by posting on Ideas · Community (microsoft.com) . This is require because as we are from community team, we can only assist you to troubleshoot the query/share work around (if we have for any by design query) and providing you required information for feature’s availability status.
This community team and Microsoft product development team are separate. So for feature’s suggestion or by design query, user need to submit feedback from their side to Microsoft product team. Once user send feedback via above mentioned way, it’s sent to Microsoft directly and it's routed to the relevant product teams who can review it.
To check more details about how to submit feedback, kindly refer this article Learn about how to provide feedback to Microsoft - Microsoft 365 admin | Microsoft Learn
Thanks for your precious time and your understanding would be highly appreciated. Have a nice day!
Best regards,
Allen | Community Moderator