they're unnecessary since https://github.com/NixOS/nixpkgs/pull/161739/files
which links the schemas to their correct fhs locations and adds
gsettings-desktop-schemas and hicolor-icon-theme to appimage fhs
The upgrade apparently made it necessary to also add `XDG_DATA_DIRS`
to fix the crash mentioned in the added comment.
I copied this solution from:
`pkgs/applications/misc/devdocs-desktop/default.nix`