Minor changes in Section 5.2.1

Remove this comment, as it is now irrelevant:

"Compared to the earlier versions of this standard, the name of this relationship has been changed from “used by” to “serving”, to better reflect its direction with an active verb: a service serves a user. The meaning of the relationship has not been altered. The “used by” designation is still allowed but deprecated, and will be removed in a future version of the standard."