arch-install-scripts: avoid using setuid wrappers

[SamLukeYes]

Description of changes

• Resolves https://github.com/archlinux/arch-install-scripts/issues/38

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.05 Release Notes (or backporting 22.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[SamLukeYes]

To use unshare mode before this PR is merged, expose the real mount/umount to the environment, e.g. nix-shell -p util-linux.

[abathur]

Commented in abathur/resholve#29 about a better workaround that should spare the substitute/keep/fake.

[SamLukeYes]

Commented in abathur/resholve#29 about a better workaround that should spare the substitute/keep/fake.

Thanks! It looks much better now. :)