vcl: Drop vcl/qa/cppunit/builder/demo.ui

This file was originally added in

    commit 9543bbaecf
    Date:   Mon Mar 26 12:15:22 2012 +0100

        bootstrap a ui-previewer for rendering GtkBuilder xml with vcl widgets

, but that ui-previewer was dropped in the meantime in

    commit c26ce14c2b
    Date:   Thu Dec 16 15:31:07 2021 +0000

        drop ui-previewer

and the .ui file also doesn't seem to be used otherwise.
`bin/run vcldemo` doesn't make use of it, and there is
cui/uiconfig/ui/widgettestdialog.ui for a widget test/demo
dialog by now which can probably fulfil the test/demo
purpose that the now dropped file presumably had originally.

It was added as a dependency via `gb_UIConfig_add_a11yerrors_uifiles`
earlier in

    commit 305285bd14
    Date:   Fri May 4 14:08:27 2018 +0200

        vcl: Run gla11y on demo.ui

, but the a11y issues have also been fixed in the meantime.
Just drop that dependency again.

The file is the last one still making use of <row>
attributes directly in the .ui file to define data for
a GtkListStore.

Don't do that in a demo file when this approach is not used
anywhere else in the code base any more.

For the (non-)use of <row> in . ui files, see also

    commit 3906bb7bed
    Author: Michael Weghorn <m.weghorn@posteo.de>
    Date:   Tue Mar 17 15:23:14 2026 +0100

        tdf#130857 widgettestdialog: Use GtkComboBoxText

for some more details/background.

Also, defining the tabs of a weld::Notebook/GtkNotebook
directly in the .ui file is no longer the usual approach
since most dialogs were switched to define tabs in C++
code as part of the introduction of vertical tabs, see
e.g.

    commit ce56a263a5
    Author: Michael Weghorn <m.weghorn@posteo.de>
    Date:   Tue Mar 10 11:39:29 2026 +0100

        tdf#130857 dbaccess: Don't define tab pages in .ui file

        As has been done almost everywhere else already, switch
        from defining (skeleton) tab pages in the .ui file for the
        database "Advanced Settings" dialog and adding the actual
        content only later.
        [...]

as well as commits by Heiko Tietze that switched to vertical tabs.
(The `git log -G '<child type="tab">'` output shows some.)

Change-Id: Icf3279d975729c60ffcb4cb3e7dfc2474c59e23c
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/203191
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

vcl/UIConfig_vcl.mk

@@ -31,8 +31,4 @@ $(eval $(call gb_UIConfig_add_uifiles,vcl,\
 	vcl/uiconfig/ui/openlockedquerybox \
 ))
 
-$(eval $(call gb_UIConfig_add_a11yerrors_uifiles,vcl,\
-	vcl/qa/cppunit/builder/demo \
-))
-
 # vim: set noet sw=4 ts=4: