file-browser: drop use of confirm-trash
Nautilus has removed their key as it was being (ab)used by other apps: https://gitlab.gnome.org/GNOME/nautilus/-/commit/e96aac1f6526f5373405e071703b5f18b0c728d3
This then caused gedit to crash on launch as the plug-in is enabled by default: https://gitlab.gnome.org/GNOME/gedit/-/issues/408
Fix #408 by simply assuming the default value of the key