MI docs: remove historic note

[Eli Zaretskii]

> From:  Vladimir Prus <ghost@cs.msu.su>
> Date:  Wed, 29 Nov 2006 18:52:31 +0300
> > 
> > Please just enclose the text in @ignore..@end ignore, instead of
> > removing it altogether.  If no one complains in a couple of GDB
> > releases, we will later remove it.
> 
> Why is it better than removing? The text is there in CVS in case we need to
> resurrect it.

There's no useful way to grep the CVS repository for a version that
had some specific text, especially if you don't remember the text
accurately enough, and there's no record in anything like "cvs
annotate" for when some text was deleted.  Checking out version after
version looking for something I remember only vaguely is not my idea
of fun.

So resurrecting it will not be easy.  Therefore, I'd like to be
reasonably sure no one wants it back for quite some time.  I hope you
understand and don't object.