XMI12 — Editorial: remove unnecessary hitorical references.

The XMI 1.1 specification contains numerous references to the way that
things
used to be in XMI 1.0, scattered throughout the document. For example,
on page 6-55, we see:

"xmi.uuidref: This attibute is no longer used in XMI 1.1. In XMI
1.0, its
use is described in the following paragraph".

It is not normal for OMG specs to include this kind of material.
Unless
there is a good reason for retaining it, it should be removed.

The only justification for this kind of material is if there is a
converted effort to maintain backwards compatibility; e.g. the CORBA
core describes multiple versions of the IIOP formats.