Stop granting all perms to 'admin' role

Now in Tailbone a user with 'admin' role can elevate to root, and that
will give them all perms.  But let the 'admin' role have perms of its
own during normal operation.

rattail/db/auth.py

@@ -142,11 +142,6 @@ def has_permission(session, principal, permission, include_guest=True, include_a
     else:
         roles = []
 
-    # Admin always has permission.
-    admin = administrator_role(session)
-    if admin in roles:
-        return True
-
     if include_guest:
         roles.append(guest_role(session))
     for role in roles: