Remove empty file discovered by Kornel.

Remove empty file discovered by Kornel.

Looks like an accidental commit.

> git log GuiGraphicsUi.h
commit a1cec91afaca91968b46e695533c10ad2a3f73d3
Author: André Pönitz <poenitz@gmx.net>
Date:   Fri Aug 31 05:53:55 2007 +0000

    move our stuff off the Q* namespace

    git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@19935 a592a061-630c-0410-9148-cb99ea01b6c8

That's all a rename, basically. The original file, QGraphicsUi.h, was commited at 12e5a52b92, and it was empty then, too.