How about adding a utility microflow to your app that looks for a user ‘MxAdmin’ and deletes it?
I personally would suggest keeping MxAdmin as a fallback. Say if by any chance your admins get locked from your system MxAdmin is the only account you can reset via Sprintr.
With that being said, in order to remove it in the cloud I suggest creating a grid for admins that allows them to manage Users, rather than Accounts, MxAdmin should come up in that grid. The alternative is removing the record from the User table in postgresql yourself.
Hope this helps