Drop some demos

The gtk4-icon-browser and gtk4-constraint-editor demos are basically
unmaintained, and not great showcases for GTK, so lets drop them.

docs/reference/gtk/gtk4-icon-browser.rst

@@ -1,32 +0,0 @@
-.. _gtk4-icon-browser(1):
-
-=================
-gtk4-icon-browser
-=================
-
------------------
-List themed icons
------------------
-
-:Version: GTK
-:Manual section: 1
-:Manual group: GTK commands
-
-SYNOPSIS
---------
-
-|   **gtk4-icon-browser** [OPTIONS...]
-
-DESCRIPTION
------------
-
-``gtk4-icon-browser`` is a utility to explore the icons in the current icon
-theme. It shows icons in various sizes, their symbolic variants where available,
-as well as a description of the icon and its context.
-
-OPTIONS
--------
-
-``-h, --help``
-
-  Show the application help.

docs/reference/gtk/meson.build

@@ -98,7 +98,6 @@ if get_option('build-demos')
     [ 'gtk4-demo', '1', ],
     [ 'gtk4-demo-application', '1', ],
     [ 'gtk4-widget-factory', '1', ],
-    [ 'gtk4-icon-browser', '1', ],
     [ 'gtk4-node-editor', '1', ],
   ]
 endif