path: remove XDG bullshit

Don't worry, your ~/.config/... paths are safe. This merely removes
handling of $XDG_CONFIG_DIRS for global paths.

Maybe there is a better solution for this, like still including the
"traditional" config dir. But I will leave the fine reading of this
(crappy) spec and fixing the code accordingly to someone else. So, if
anyone has interest in getting this behavior back, you will have to
write a patch. This patch should _also_ not break expected behavior.

Fixes #1060.