Revert Merge x-updates into master due to mesa bloat

See #490 discussion.

This reverts commit 1278859d3167b9f84bfab680d9c8c463adf64a60, reversing
changes made to 0c020c98f9d4f49d5c9907db5f4b35aac7df959b.

Conflicts:
	pkgs/desktops/xfce/core/xfce4-session.nix (take master)
	pkgs/lib/misc.nix (auto)