flatpak: Stop renaming icons

We are now installing properly named icons, no need to
rename anymore.

This was causing ci to fail.

build-aux/flatpak/org.gtk.Demo.json

@@ -5,7 +5,6 @@
     "sdk": "org.gnome.Sdk",
     "command": "gtk4-demo",
     "tags": ["devel", "development", "nightly"],
-    "rename-icon": "gtk4-demo",
     "desktop-file-name-prefix": "(Development) ",
     "finish-args": [
         "--device=dri",

build-aux/flatpak/org.gtk.WidgetFactory.json

@@ -5,7 +5,6 @@
     "sdk": "org.gnome.Sdk",
     "command": "gtk4-widget-factory",
     "tags": ["devel", "development", "nightly"],
-    "rename-icon": "gtk4-widget-factory",
     "desktop-file-name-prefix": "(Development) ",
     "finish-args": [
         "--device=dri",