in SU01 I would delete a Company address.
It seems only possible to "Assign other company address" or "Assign new company address".
I would only delete old company adress but there is not a button to delete it.
Every user is assigned to one company code address as reference while creating user ID. It is not possible to delete the compancy code assignment, but you can change the assignment by either assign other company code or assign new company code.