wrap-setup: Don't revert environment variables we already changed
Now that pv-runtime and pv_bind_and_propagate_from_environ() both want to modify XDG_DATA_DIRS, they'll fight: pv-runtime alters XDG_DATA_DIRS, and then pv_bind_and_propagate_from_environ() alters it back again.
For Flatpak users, this manifested as an inability to load some (all?)
Vulkan layers in the pressure-vessel sub-sandbox, because
/usr/lib/pressure-vessel/overrides/share is prepended to the search path
but then discarded. Non-Flatpak users will not usually be affected,
although in principle they might be if their XDG_DATA_DIRS contains
non-canonical paths like /opt/lib/../share
.
This fixes a regression in 0.20240301.0.
Resolves: https://github.com/ValveSoftware/steam-runtime/issues/662
Fixes: 8d76938e "pv-wrap: Explicitly share $XDG_CONFIG_HOME, etc. if sharing $HOME"