Update the kadm5.acl example

Make the example and documentation a closer match to reality.
In particular, the list permission is all-or-nothing; it is not
restricted in scope by the target_principal field.  Change the
table entry to try and indicate this fact, and do not put list
permissions on any example line that is scoped by a target_principal
pattern.

While here, remove the nonsensical granting of global inquire
permissions to */* (inaccurately described as "all principals"),
and the granting of privileges to foreign-realm principals.
It is not possible to obtain an initial ticket (as required by
the kadmin service) for a principal in a different realm, and
the current kadmind implementation can serve only a single realm
at a time -- this permission literally has no effect.  Replace
it with a (presumably automated) "Service Management System"
example, where it might make sense to limit the principals which
are automatically created.