[doc patch] Remove --xdb

[Eli Zaretskii]

> Date: Sat, 11 Apr 2015 19:06:41 +0200
> From: Jan Kratochvil <jan.kratochvil@redhat.com>
> Cc: Yao Qi <yao@codesourcery.com>, gdb-patches@sourceware.org,
>         Joel Brobecker <brobecker@adacore.com>,
>         Pedro Alves <palves@redhat.com>
> 
> > I think this should have a NEWS entry.  Could you prepare one?
> 
> OK for check-in (merged with the other patch), Eli?

Yes, thanks.