home-manager.useGlobalPkgs: default to true

[teto]

Description

home-manager.useGlobalPkgs is true by default and will become ineffective after 26.11. Using a different set of pkgs for home-manager and nixos has been a constant source of confusion for newcomers and does not make a lot of sense so we are getting rid of this option.

I can't see a usecase for it so if you use this knowingly, let me know why please.

Checklist

• Change is backwards compatible.

• Code formatted with nix fmt or
  nix-shell -p treefmt nixfmt deadnix keep-sorted --run treefmt.

• Code tested through nix run .#tests -- test-all or
  nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.
  • Generate a news entry. See News
  • Basic tests added. See Tests

• If this PR adds an exciting new feature or contains a breaking change.

  • Generate a news entry. See News