MI docs: remove historic note

[Eli Zaretskii]

> From: Vladimir Prus <vladimir@codesourcery.com>
> Date: Wed, 15 Nov 2006 17:35:25 +0300
> 
> This patch removes that text. Now section on variable object starts with 
> explanation what is variable object -- which looks quite reasonable.
> 
> OK?

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.

Thanks.