pv-wrap: Don't make XDG_CONFIG_DIRS, XDG_DATA_DIRS available in container
Unlike XDG_CONFIG_HOME and XDG_DATA_HOME, these search paths are expected to be read-only, making it much less likely that a game or app component will misbehave if they contain a dangling symlink.
Also unlike XDG_CONFIG_HOME and XDG_DATA_HOME, these paths are much more likely to contain OS-related path elements that can cause container runtime regressions, such as /var/cache (steamrt/tasks#434) and /var/lib (steamrt/tasks#493).
A regression risk with this change is that if a user has set for example
XDG_DATA_DIRS=/offload/data:/usr/local/share:/usr/share, since
0.20240301.0 the result has been that /offload/data has been shared
with the container, which means apps and games in a SLR container will
load icons, .desktop files, etc. from that location. No longer doing
this is both good and bad. It's good because it makes the container
more self-contained again, but it's bad because users might have come
to rely on /offload/data being available, which would no longer be
the case after this change.
steamrt/tasks#493
Ready for review, but needs some thought about whether the risk of additional regressions similar to steamrt/tasks#434, steamrt/tasks#493 outweighs the risk that a user has come to rely on their XDG_CONFIG_DIRS and XDG_DATA_DIRS getting into the container, and as a result encounters a regression as a result of this change.