Revert "Put /nix/var/nix/{temproots,userpool} on a tmpfs"

This reverts commit dd49094a25057211d77a3dc4d075a749db748139. Nix
barfs if /nix/var/nix/temproots is a symlink :-(
Improve gpm service
switch-to-configuration: Handle systemctl output change
Set $LOCALE_ARCHIVE in all systemd units

This variable used to be inherited implicitly from the stage-2 script,
but systemd now clears the environment. So we need to set it
explicitly.