steam: drop gnome2.GConf dependency•••GConf depends on ORBit2 which no longer compiles on https://github.com/NixOS/nixpkgs/pull/340612
ORBit2 / GConf are EOL/Archived:
- https://gitlab.gnome.org/Archive/orbit2 (last commit on main branch 8 years ago)
- https://gitlab.gnome.org/Archive/gconf (last commit on main branch 8 years ago)