Hi,
You can delete admin account with delete account
But i didn't see before deleting a user account
But I think in your case,no need for that,all can be done through web
Check only if this name is configured in any other place in the cucm
I think you may have it configured as a Remote Destination Profile or something like that
If you tired searching,add your device profile with the needed name and add extra letter at beggining or end of it which won't affect any thing for your user,he isn't using this profile name at all
ex: [ HIS NAME DP ]
wish this be helpful
thanks